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Abstract:

A toner with good low-temperature fixability even in light-pressure type
fixing units, which causes no contamination of fixing films and provides
images having stable image densities and excellent image quality after
long-term use. The toner includes a toner particle containing a binder
resin, a coloring agent, a release agents (a) and (b) The release agent
(a) is a monofunctional or bifunctional ester wax; the release agent (b)
is a hydrocarbon wax; a solubility of the release agent (a) into the
binder resin is higher than that of the release agent (b). When
tetrahydrofuran-soluble components of the toner are subjected to GPC, a
proportion of components having a molecular weight of 500 or less is 2.5
area % or less. When the tetrahydrofuran-soluble components at 25°
C. are subjected to SEC-MALLS, a weight-average molecular weight Mw
thereof is 5,000-100,000, and the Mw and the radius of gyration Rw
thereof satisfy
5.0×10-4≦Rw/Mw≦1.0×10-2.

Claims:

1. A toner comprising toner particles, each of which contains a binder
resin, a coloring agent, a release agent (a), and a release agent (b),
wherein: (1) the release agent (a) is a monofunctional or bifunctional
ester wax; (2) the release agent (b) is a hydrocarbon wax; (3) a
solubility of the release agent (a) into the binder resin is higher than
a solubility of the release agent (b) into the binder resin; (4) when
tetrahydrofuran-soluble components of the toner are subjected to
measurement by gel permeation chromatography (GPC), a proportion of
components having a molecular weight of 500 or less is 2.5 area % or
less; and (5) when tetrahydrofuran-soluble components of the toner at
25.degree. C. are subjected to measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS), a
weight-average molecular weight Mw thereof is 5,000 or more and 100,000
or less, and the weight-average molecular weight Mw and an radius of
gyration Rw thereof satisfy the following equation 1.5.0.times.10.sup.-4.ltoreq.Rw/Mw≦1.0.times.10.sup.-2 Eq. 1

2. A toner according to claim 1, wherein: when the
tetrahydrofuran-soluble components of the toner at 25.degree. C. are
subjected to the measurement by size exclusion chromatography-multiangle
laser light scattering (SEC-MALLS), the weight-average molecular weight
Mw is 5,000 or more and 25,000 or less; and the weight-average molecular
weight Mw and the radius of gyration Rw satisfy the following equation 2.2.0.times.10.sup.-3.ltoreq.Rw/Mw≦1.0.times.10.sup.-2 Eq. 2

3. A toner according to claim 1, wherein the toner has an average
circularity of 0.960 or more.

4. A toner according to claim 1, wherein a total energy of the toner
particle as measured with a powder flowability analyzer when a propeller
type blade is caused to penetrate a toner particle layer at an agitation
rate of 100 mm/sec is 500 mJ or more and 1,000 mJ or less.

5. A toner according to claim 1, wherein the release agent (a) is a
monofunctional or bifunctional ester wax having an acid value of 2
mgKOH/g or less and a peak top temperature of a maximum endothermic peak
of 60.degree. C. or more and 80.degree. C. or less.

6. A toner according to claim 1, wherein the binder resin comprises, as a
main component, a resin obtained by polymerizing a polymerizable monomer
with a peroxydicarbonate.

7. A toner according to claim 1, wherein a relationship
0.ltoreq.(Tmb-Tma)≦5 is satisfied, where a peak top temperature of
a maximum endothermic peak of the release agent (a) and a peak top
temperature of a maximum endothermic peak of the release agent (b) in
differential scanning calorimetry (DSC) of the toner are respectively
represented by Tma (° C.) and Tmb (° C.).

8. A toner according to claim 1, wherein: the release agent (a) is
incorporated in an amount of 5 parts by mass or more and 20 parts by mass
or less with respect to 100 parts by mass of the binder resin; and a mass
ratio between contents of the release agent (a) and the release agent
(b), (content of the release agent (a))/(content of the release agent
(b)), is 1/1 or more and 20/1 or less.

9. A toner according to claim 1, wherein the toner particle is produced
by a suspension polymerization method.

10. A toner according to claim 1, wherein a ratio Mn(135.degree.
C.)/Mn(25.degree. C.) between a number-average molecular weight
Mn(25.degree. C.) when the tetrahydrofuran-soluble components of the
toner at 25.degree. C. are subjected to the measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS) and a
number-average molecular weight Mn(135.degree. C.) when
o-dichlorobenzene-soluble components of the toner at 135.degree. C. are
subjected to measurement by size exclusion chromatography-multiangle
laser light scattering (SEC-MALLS) is less than 25.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a toner to be used in, for
example, an electrophotographic method, an electrostatic recording
method, and a magnetic recording method.

BACKGROUND ART

[0002] A general electrophotographic image-forming method provides a toner
image as described below by utilizing, for example, a photoconductive
substance. An electrical latent image is formed on an electrostatic
latent image-bearing member by various means. Next, the latent image is
visualized by being turned into a toner image through development by a
developing apparatus. Next, the toner image is transferred onto a
transfer material such as paper as required, and is then fixed with heat,
pressure, heat and pressure, or solvent vapor. An image-forming apparatus
for such method is, for example, a copying machine or a printer.

[0003] A reduction in the size of the main body of a copying machine or
printer employing the electrophotographic method has been requested in
recent years in consideration of energy savings and space savings. In
addition, meanwhile, such high durability as described below has been
requested of the copying machine or printer. Namely, it is required that
no reduction in image quality occurs even after images have been copied
or printed on a large number of sheets.

[0004] One method for the reduction in the size of the main body of any
such image-forming apparatus is the simplification of a fixing apparatus.
The simplification of the fixing apparatus is, for example, film fixation
that facilitates the simplification of a heat source and the construction
of the apparatus. In the film fixation, the simplification of the heat
source and the construction of the apparatus are facilitated. In
addition, good thermal conductivity is obtained as a result of the use of
a film as a fixing member. Accordingly, a first printout time can be
shortened. However, the film is used while being pressed against a roller
under a relatively high pressure, and hence a problem such as the wear of
the film at the time of its long-term use is apt to arise.

[0005] A toner that shows good fixability even under a light pressure has
been requested for suppressing such problem. In addition, meanwhile, an
ability to perform development with improved stability has been requested
of the toner, and an improvement in terms of such developing performance
as described below has also been requested of the toner. A high image
density and high image quality can be obtained even at the time of its
long-term use.

[0006] Investigations from various aspects such as a toner structure and
the improvement of a release agent have been conducted on such problems
as described above concerning, for example, the fixability of the toner
and development stability at the time of its long-term use.

[0007] Proposed in Patent Literature 1 are a polymerized toner of such a
core-shell type structure that core particles formed of colored polymer
particles each containing a polyfunctional ester compound, a
Fischer-Tropsch wax, and a coloring agent are each covered with a shell
formed of a polymer having a glass transition temperature higher than the
glass transition temperature of a polymer component that forms each of
the core particles, in which the usage ratio between the polyfunctional
ester compound and the Fischer-Tropsch wax is 5/5 to 29/1, and a method
of producing the toner.

[0008] In addition, Patent Literature 2 proposes a method of producing a
toner including polymerizing a polymerizable monomer composition having
at least a polymerizable monomer and a coloring agent in an aqueous
medium, the method of producing a toner being characterized in that a
peroxide-based initiator of a dicarbonate type is used as a
polymerization initiator.

[0009] In addition, Patent Literature 3 proposes a magnetic toner having
toner particles each containing at least a binder resin, a wax, and a
magnetic powder, and an inorganic fine powder, the magnetic toner being
characterized in that the toner particles have an average circularity of
0.960 or more, that substantially no magnetic powder is exposed to the
surface of each toner particle, and that the wax has at least two
endothermic peaks in differential calorimetry, one of the endothermic
peaks is present in the range of 40 to 90° C., and the other is
present in the range of 70 to 150° C.

[0010] Although fixability is improved in an ordinary fixing unit
construction by each of those toners, each of those toners has showed
insufficient fixability in the film fixation of a light-pressure type
like the present invention. In addition, the following new problem has
become recognized. The releasability of each of the toners from the
fixing member reduces probably owing to the fact that the fixing unit
construction of the present invention is of a light-pressure type, and
hence the contamination of the fixing film occurs. Further, the toners
each still have had room for improvements in image density and image
quality at the time of its long-term use as well.

CITATION LIST

Patent Literature

[0011] PTL 1: Japanese Patent No. 03440983

[0012] PTL 2: Japanese Patent
Application Laid-Open No. 2006-343372

[0013] PTL 3: Japanese Patent
Application Laid-Open No. 2002-072540

SUMMARY OF INVENTION

Technical Problem

[0014] An object of the present invention is to provide a toner that has
solved such problems as described above. That is, the object of the
present invention is to provide a toner that shows good low-temperature
fixability even in a light-pressure type fixing unit construction and can
reduce the contamination of a fixing film. Another object of the present
invention is to provide a toner with which an image having a stable image
density and excellent image quality can be developed even after its
long-term use.

Solution to Problem

[0015] The present invention relates to a toner, including a toner
particle containing a binder resin, a coloring agent, a release agent
(a), and a release agent (b), in which:

(1) the release agent (a) is a monofunctional or bifunctional ester wax;
(2) the release agent (b) is a hydrocarbon wax; (3) a solubility of the
release agent (a) into the binder resin is higher than a solubility of
the release agent (b) into the binder resin; (4) when
tetrahydrofuran-soluble components of the toner are subjected to
measurement by gel permeation chromatography (GPC), a proportion of
components having a molecular weight of 500 or less is 2.5 area % or
less; and (5) when tetrahydrofuran-soluble components of the toner at
25° C. are subjected to measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS), a
weight-average molecular weight Mw thereof is 5,000 or more and 100,000
or less, and the weight-average molecular weight Mw and a radius of
gyration Rw thereof satisfy the following equation 1.

5.0×10-4≦Rw/Mw≦1.0×10-2 Eq. 1

Advantageous Effects of Invention

[0016] According to the present invention, it is possible to provide the
toner that shows good low-temperature fixability even in a light-pressure
type fixing unit construction and can reduce the contamination of a
fixing film. It is also possible to provide the toner with which an image
having a stable image density and excellent image quality can be
developed even after its long-term use.

BRIEF DESCRIPTION OF DRAWINGS

[0017]FIG. 1 is a schematic sectional view illustrating an example of an
image-forming apparatus in which a toner of the present invention can be
suitably used.

[0019] FIGS. 3A and 3B are each an explanatory diagram of a blade portion
of an apparatus to be used in the measurement of the total energy of
toner particles.

[0020]FIG. 4 is an explanatory diagram of a pattern of checkers to be
used in an evaluation for dot reproducibility.

DESCRIPTION OF EMBODIMENTS

[0021] The present invention relates to a toner, and a conventionally
known electrophotographic process can be applied to each of an
image-forming method and a fixing method without any particular
limitation.

[0022] Investigations conducted by the inventors of the present invention
have found that none of a mere reduction in the molecular weight of a
binder resin, a mere reduction in the glass transition temperature of the
binder resin, and mere incorporation of a large amount of a release agent
suffices for an improvement in fixability in a light-pressure type fixing
unit construction. First, when the improvement of the binder resin such
as the reduction in the molecular weight of the binder resin or the
reduction in its glass transition temperature is performed, such a
tendency that the viscoelasticity of the binder reduces and the
low-temperature fixability of a toner is improved is observed indeed.
However, a fixing pressure is low in the light-pressure type fixing unit
construction, and hence the toner cannot sufficiently deform and dot
reproducibility reduces. In addition, heat hardly propagates through the
toner in a uniform fashion owing to the low fixing pressure, and hence
the uniformity of the density of an image formed with the toner reduces.
Further, a fixation failure (so-called fixation offset) occurs, and hence
a fixing film is contaminated in some cases.

[0023] Next, when the release agent is incorporated in a large amount, the
plasticity and releasability of the toner tend to be improved. However,
the fixing pressure is low in the light-pressure type fixing unit
construction even when the release agent is incorporated in a large
amount. Accordingly, the toner cannot sufficiently deform and the dot
reproducibility reduces. In addition, a balance cannot be established
between the plasticity and the releasability. As a result, the fixation
failure is apt to occur, and hence the fixing film is contaminated in
some cases.

[0024] Further, even a toner obtained by combining the above-mentioned
cases, i.e., the improvement of the binder resin and the incorporation of
a large amount of the wax is still in an insufficient state because the
dot reproducibility reduces, or an image suffering from a fixation
failure or low density uniformity is obtained.

[0025] In addition, a toner with its fixability improved by any such
existing technique as described above is poor in image stability at the
time of its long-term use, and its influences on an image such as a
reduction in density and a reduction in image quality are observed. In
addition, owing to the mere reduction in the molecular weight of the
binder resin, the mere reduction in the glass transition temperature of
the binder resin, or the mere incorporation of a large amount of the
release agent (a) reduction in the developability of the toner occurs in
some cases after the toner has been left to stand under a
high-temperature, high-humidity environment. The foregoing suggests that
the toner still has room for improvement to simultaneously achieve both
fixability and developability.

[0026] Further, the inventors of the present invention have continued
extensive studies, and as a result, have found that a toner extremely
excellent in plasticity and releasability can be obtained by controlling
the molecular weight and branched structure of a binder resin, and
selecting such a release agent (a) and a release agent (b) as described
below. The release agent (a) easily exists in a state of being
compatibilized with the binder resin in the toner and has excellent
plasticity, and the release agent (b) easily exists in such a state as to
form a domain in the toner and has excellent releasability. Further, it
has also been elucidated that the sharp melt property of the toner can be
significantly improved by the control and selection. Thus, the toner can
show good fixability even in a light-pressure type fixing unit
construction.

[0027] The inventors of the present invention have considered that the
fact that such results were obtained is attributable to the following
reasons.

[0028] The plasticization of the toner and an improvement in its
releasability are important conditions necessary for improving fixability
in a light-pressure type fixing unit construction.

[0029] In the present invention, a monofunctional or bifunctional ester
wax and a hydrocarbon wax are used in combination as release agents. When
the release agents are used together with a styrene-acrylic resin,
polyester resin, or the like to be generally used as a binder resin, the
monofunctional or bifunctional ester wax mainly plasticizes the binder
resin to improve the low-temperature fixability of the toner, and the
hydrocarbon wax mainly improves the releasability of the toner.

[0030] It has been found that the present invention provides, by combining
those release agents with a specific binder resin as a feature of the
present invention, an effect that cannot be expressed when each of the
release agents is used alone or when the respective release agents are
combined with a conventional binder resin while the release agents are
used in combination.

[0031] The binder resin to be used in the toner of the present invention
satisfies the following conditions (i) and (ii):

(i) when the tetrahydrofuran-soluble components of the toner are
subjected to measurement by gel permeation chromatography (GPC), a
proportion of components having a molecular weight of 500 or less is 2.5
area % or less; and (ii) when the tetrahydrofuran-soluble components of
the toner are subjected to measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS), their
weight-average molecular weight Mw is 5,000 or more and 100,000 or less,
and the weight-average molecular weight Mw and their radius of gyration
Rw satisfy the relationship of
5.0×10-4≦Rw/Mw≦1.0×10-2.

[0032] It is insufficient that the binder resin to be used in the toner of
the present invention merely has a low molecular weight, and it is
important to control the branched state of the molecular chain of the
binder resin as well. That is, an object of the present invention is
achieved by the fact that the tetrahydrofuran-soluble components of the
toner of the present invention each do not have a branched type molecular
structure but have a molecular structure close to a linear type. The
adoption of a molecular structure close to a linear type molecular
structure improves the thermoplasticity of the toner, thereby enabling
the toner to sharply melt. It should be noted that in the present
invention, the branched state of the binder resin in the toner is
specified on the basis of the branched state of each
tetrahydrofuran-soluble component of the toner, provided that the toner
may contain a tetrahydrofuran-insoluble component as long as its content
is 40 mass % or less of the binder resin.

[0033] Further, the dispersibility of the monofunctional or bifunctional
ester wax that easily imparts plasticity in the binder resin is markedly
improved by controlling the molecular weight and branched state of the
binder resin like the present invention. This is because of the following
reason. When the monofunctional or bifunctional ester wax is introduced
into the binder resin having a linear type molecular structure and in a
state of being reduced in molecular weight, the monofunctional or
bifunctional ester wax itself is also of a linear type molecular
structure and hence made to easily enter the binder resin. That is, such
a state that the monofunctional or bifunctional ester wax and the binder
resin easily become compatible with each other is established, and hence
the dispersibility of the monofunctional or bifunctional ester wax is
improved. In addition, with regard to the hydrocarbon wax, when the
hydrocarbon wax is used alone for a binder resin to be generally used in
a toner, the releasability of the toner is improved, but part of the
hydrocarbon wax is compatibilized with the binder resin, and hence the
releasability of the hydrocarbon wax is not exerted to the maximum.
However, when the monofunctional or bifunctional ester wax exists, the
monofunctional or bifunctional ester wax having a large solubility in the
binder resin is preferentially compatibilized with the binder resin, and
hence the hydrocarbon wax having relatively high hydrophobicity easily
forms a domain.

[0034] As described above, when the binder resin having a linear type
molecular structure and reduced in molecular weight, and the
monofunctional or bifunctional ester wax and the hydrocarbon wax with a
controlled relationship between their solubilities in the binder resin
exist, each toner component exists in a suitable state, and hence an
improvement in fixability that has never been achieved before can be
observed.

[0035] Accordingly, with regard to the toner, the monofunctional or
bifunctional ester wax is dispersed in the toner, and the hydrocarbon wax
can exist in such a state as to form a domain near the center of the
toner. With such toner structure, upon reception of heat by the toner at
the time of fixation, the plasticization of the toner mainly by the
dispersion of the monofunctional or bifunctional ester wax in the binder
resin is additionally promoted, and hence the toner is rapidly deformed.

[0036] Further, it has been elucidated that as a result of the
deformation, the hydrocarbon wax present in the toner, the wax being
present mainly as a domain, is easily extruded to the outside of the
toner, the releasability of the toner is easily expressed, and the
contamination of a fixing film is suppressed.

[0037] In addition, it has been elucidated that controlling the structure
of the toner with such binder resin and release agents as described above
additionally improves the dot reproducibility and the effect is sustained
even at the time of the long-term use of the toner.

[0038] The foregoing can be achieved probably as described below. The
molecular weight distribution and branched state of the binder resin, and
the states of presence of the release agents are optimized, and hence the
charged state of the toner is uniformized. Further, an image well
consistent with a dot is obtained probably because of the following
reason. The image can be fixed even under a light pressure at the time of
the fixation, and hence the toner does not excessively squash at the time
of the fixation.

[0039] In addition, the toner of the present invention has shown a good
result concerning its developability after standing under a
high-temperature, high-humidity environment as well. This is because of
the following reason. Despite the fact that the binder resin with its
molecular weight reduced is used, the combination of the binder resin
having a small extent of branching with the release agent (a) and the
release agent (b) results in an interaction among the binder resin, and
the release agent (a) and the release agent (b) even under the
high-temperature, high-humidity environment, and hence the storage
stability of the toner is improved. Accordingly, a problem such as the
exudation of the release agents and a low-molecular weight component in
the binder resin to the surface of the toner hardly occurs even at the
time of the standing under the high-temperature, high-humidity
environment, and hence the toner can maintain good chargeability even
after the standing under the high-temperature, high-humidity environment.
Thus, the developability is improved.

[0040] The toner of the present invention has the monofunctional or
bifunctional ester wax as the release agent (a). The monofunctional or
bifunctional ester wax is an ester wax having a linear type molecular
structure, and easily conforms to the binder resin having a linear type
molecular structure. Accordingly, the monofunctional or bifunctional
ester wax can be uniformly dispersed in the toner, and as a result,
easily imparts the plasticity of the toner. On the other hand, an ester
wax that is trifunctional or more is of a branched molecular structure
because the wax has three or more ester bonds. Accordingly, its
compatibilizing performance with respect to the binder resin having a
linear type molecular structure is apt to reduce, and hence the wax is
apt to be dispersed in the toner nonuniformly. As a result, the
plasticity is apt to reduce. Further, the wax is less compatible with the
resin upon its dissolution at the time of the fixation as well, and hence
the plasticity reduces.

[0041] Here, the binder resin to be used in the present invention is
preferably a styrene-based copolymer or polyester resin having a linear
type molecular structure, particularly preferably a styrene-based
copolymer using styrene as a main component. Further, when the resin is a
styrene-based copolymer having a linear type molecular structure, the
dispersed states of the monofunctional or bifunctional ester wax and the
hydrocarbon wax are easily adjusted.

[0042] Next, the toner of the present invention has the hydrocarbon wax as
the release agent (b). In general, hydrocarbon waxes having polarity is
rare and the waxes have extremely high hydrophobicity, and hence any such
wax easily forms a domain in the toner. Accordingly, when the toner is
produced by, for example, a suspension polymerization method, the
hydrocarbon wax easily forms a domain near the center of the toner.

[0043] Here, the presence of the release agent (a) having good
compatibilizing performance with respect to the binder resin together
with the release agent (b) like the present invention allows the release
agent (b) having low compatibilizing performance with respect to the
binder resin to further easily form a domain, and hence a toner structure
suitable for the present invention can be achieved.

[0044] As described above, the hydrocarbon wax has low compatibilizing
performance with respect to the binder resin, and hence the wax can exude
from the toner at the time of its dissolution caused by heat of fixation
to impart releasability from a fixing member. Accordingly, good fixation
can be performed even in a light-pressure type fixing unit construction.

[0045] In the present invention, a solubility in the binder resin was used
as an indicator of the conforming performance of any such release agent
as described above to the binder resin.

[0046] That is, in the present invention, the solubility of the release
agent (a) in the binder resin needs to be higher than the solubility of
the release agent (b) in the binder resin. When the solubility of the
release agent (a) in the binder resin is higher than the solubility of
the release agent (b) in the binder resin, the release agent (a) easily
comes compatible with the binder resin, and is hence brought into a state
of being finely dispersed in the binder resin. Further, the release agent
(b) hardly comes compatible with the binder resin relatively, and hence
easily forms a domain.

[0047] Controlling the solubilities of the release agent (a) and the
release agent (b) in the binder resin as described above enables the
toner to sufficiently exert its releasability and plasticity.

[0048] Of such release agents a, a monofunctional or bifunctional ester
wax having an acid value of 2 mgKOH/g or less and a peak top temperature
of a maximum endothermic peak of 60° C. or more and 80° C.
or less is particularly preferred. When the acid value is 2 mgKOH/g or
less, the compatibilizing performance with respect to the binder resin is
easily improved. In addition, in the case where the toner is produced in
an aqueous medium, when the acid value is 2 mgKOH/g or less, the release
agent (a) hardly exudes to the surface of the toner, and hence the
storage stability and chargeability of the toner are easily improved.

[0049] When the peak top temperature of the maximum endothermic peak of
the release agent (a) is 60° C. or more, the storage stability and
the chargeability are further easily improved. In addition, when the peak
top temperature is 80° C. or less, the low-temperature fixability
is further easily improved.

[0050] It should be noted that the release agent (a) is preferably
incorporated in an amount of 5 parts by mass or more and 20 parts by mass
or less with respect to 100 parts by mass of the binder resin. In
addition, the mass ratio between the contents of the release agent (a)
and the release agent (b) (content of the release agent (a)/content of
the release agent (b)) preferably falls within the range of 1/1 or more
and 20/1 or less. In addition, the total content of the release agents in
toner particles in the present invention is preferably 5 parts by mass or
more and 40 parts by mass or less with respect to 100 parts by mass of
the binder resin.

[0051] In addition, when the peak top temperature of the maximum
endothermic peak of the release agent (a) and the peak top temperature of
the maximum endothermic peak of the release agent (b) in the differential
scanning calorimetry (which may hereinafter be referred to as "DSC") of
the toner are represented by Tma (° C.) and Tmb (° C.),
respectively, the relationship of 0≦(Tmb-Tma)≦5 is
preferably satisfied. When the relationship of
0≦(Tmb-Tma)≦5 is satisfied, the monofunctional or
bifunctional ester wax that largely contributes to the meltability of the
toner easily melts prior to the hydrocarbon wax that easily contributes
to the releasability. After that, the toner can exert the releasability.
Accordingly, the low-temperature fixability and the releasability are
easily improved. In addition, the case where the difference between the
peak top temperature of the maximum endothermic peak of the hydrocarbon
wax and the peak top temperature of the maximum endothermic peak of the
monofunctional or bifunctional ester wax is 5° C. or less is
preferred because the melting and the release easily occur at the same
time.

[0052] It should be noted that a method involving melting the release
agent (a) and the binder resin, and then gradually lowering their
temperatures at the time of the production of the toner is preferred for
establishing such a state that the release agent (a) and the binder resin
are compatibilized with each other because of its simplicity.
Specifically, the rate of temperature decrease in a cooling step for
terminating a polymerization reaction step is preferably 10°
C./min or less, more preferably 6° C./min or less, still more
preferably 3° C./min or less. In addition, the toner particles are
preferably produced in an aqueous medium from such a viewpoint that such
cooling step is easily managed.

[0053] Next, it is important that the toner of the present invention be
such that when the tetrahydrofuran-soluble components of the toner are
subjected to measurement by gel permeation chromatography (GPC), the
proportion of components having a molecular weight of 500 or less is 2.5
area % or less.

[0054] When the proportion of ultra-low-molecular weight components having
a molecular weight of 500 or less in the tetrahydrofuran-soluble
components of the toner is 2.5 area % or less, a difference between the
local compatibilities of the release agent (a) in the binder resin
becomes small, and hence such a tendency that the dispersibility of the
release agent (a) in the toner becomes uniform and the fixability is
improved is observed. Further, a reduction in the amount of the
ultra-low-molecular weight component results in improvements in the
chargeability, and the density and image quality of an image formed with
the toner. In addition, a change over time of the ultra-low-molecular
weight components and the like are eliminated, and hence the toner
changes to a small extent at the time of its long-term use and can
provide a high density and high image quality over a long time period.
When the proportion of the components having a molecular weight of 500 or
less is larger than 2.5 area %, the molecular weight distribution of the
resin component of the binder resin as a whole enlarges, and hence the
plasticization of the binder resin is apt to be nonuniform upon reception
of heat at the time of fixation, and density unevenness and a fixation
failure are apt to occur. In addition, the dispersibility of the release
agent (a) reduces, and hence the plasticity tends to reduce additionally.

[0055] It should be noted that the proportion of the ultra-low-molecular
weight components in the tetrahydrofuran-soluble components of the toner
of the present invention was measured by gel permeation chromatography
(GPC). On the other hand, the weight-average molecular weight Mw and the
radius of gyration Rw are measured by size exclusion
chromatography-multiangle laser light scattering (which may hereinafter
be referred to as "SEC-MALLS"). The employment of size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS) can provide
a detailed data on a molecular structure such as the radius of gyration
Rw.

[0056] It should be noted that the setting of the proportion of the
components having a molecular weight of 500 or less in the
tetrahydrofuran-soluble components of the toner in the present invention
to 2.5 area % or less can be achieved by changing the kind and amount of
a polymerization initiator, and a reaction condition. The polymerization
initiator is preferably, for example, such a kind as described below. The
polymerization initiator has high reactivity and produces a single
radical species upon its cleavage. When the reactivity is high, the
polymerization reaction easily progresses, and hence the production of
the ultra-low-molecular weight components is easily suppressed. In
addition, in the case where only a single radical species is produced, a
variation in reactivity hardly occurs as compared with that in the case
where different radicals are produced, and hence the molecular weight of
the resin is easily adjusted.

[0057] Next, it is important that the toner of the present invention be
such that when the tetrahydrofuran-soluble components of the toner are
subjected to measurement by size exclusion chromatography-multiangle
laser light scattering (SEC-MALLS), the weight-average molecular weight
Mw is 5,000 or more and 100,000 or less, and the ratio Rw/Mw between the
weight-average molecular weight Mw and the radius of gyration Rw is
5.0×10-4 or more and 1.0×10-2 or less. A unit used
for the radius of gyration is "nm".

[0059] The abundance of each molecular size can be determined by
measurement based on SEC (ordinary GPC). In contrast, in SEC-MALLS
(apparatus obtained by coupling SEC as separating means and a multiangle
light scattering detector), a more real molecular weight distribution
which reflects a difference in molecular structure such as branching or
crosslinking can be determined for a mixed sample formed of molecules of
the same molecular size by utilizing light scattering. In addition, a
mean square radius (Rg2) that represents the extension per molecule
can be determined. Thus, the molecular design of the toner can be
accurately performed.

[0060] In a conventional SEC method, molecules to be subjected to
measurement undergo a molecular sieve effect upon their passage through a
column, and are then sequentially eluted in the order of decreasing
molecular size. Thus, their molecular weights are measured. In this case,
comparing a linear polymer and a branched polymer having an equal
molecular weight, the former is eluted more quickly because the former
has the larger molecular size in a solution. Therefore, the molecular
weight of the branched polymer measured by the SEC method is measured to
be smaller than its molecular weight obtained by the SEC-MALLS method.

[0061] On the other hand, the Rayleigh scattering of a molecule to be
subjected to measurement was utilized in the light scattering method of
the present invention.

[0062] A molecular weight even closer to the true molecular weight
(absolute molecular weight) can be determined in each of all molecular
forms, i.e., a linear polymer and a branched polymer, by measuring the
dependencies of the intensity of scattered light on the incidence angle
of light and a sample concentration, and analyzing the measured results
by, for example, a Zimm method or a Berry method. In the present
invention, the intensity of scattered light was measured by the SEC-MALLS
measurement method, and a relationship represented by Zimm's equation
below was analyzed by utilizing a Debye plot so that the weight-average
molecular weight (Mw) and the mean square radius (Rg2) based on the
absolute molecular weight were derived. In addition, the Debye plot is a
graph obtained by plotting KC/R(θ) indicated by the axis of
ordinate against sin2(θ/2) indicated by the axis of abscissa,
and an Mw (weight-average molecular weight) and a mean square radius
Rg2 can be calculated from the intercept of the axis of ordinate and
the gradient at that time, respectively.

[0063] It should be noted that the number-average molecular weight Mn, the
weight-average molecular weight Mw and mean square radius Rg2 are
calculated for each component of elution time. Accordingly, in order that
the number-average molecular weight Mn, weight-average molecular weight
Mw and mean square radius Rg2 of the entire sample be calculated,
each of their average values must be further calculated.

[0064] It should be noted that when measurement is performed with an
apparatus to be described later, values for the number-average molecular
weight (Mn), weight-average molecular weight (Mw), and radius of gyration
(Rw) of the entire sample are obtained as direct outputs from the
apparatus.

[0065] Here, mean square radius Rg2 is a value that generally
represents the extension per molecule, and the value Rw/Mw given by
dividing a root value of the radius of gyration Rw
(Rw=(Rg2)1/2) by the Mw is taken to represent the degree of
branching per molecule.

[0066] In other words, as the Rw/Mw reduces, the spread becomes smaller
for the molecular weight, and hence the extent of branching of each
molecule enlarges. In contrast, as the Rw/Mw increases, the spread
becomes larger for the molecular weight, and hence the molecule is
considered to be linear.

[0067] In the present invention, it is important that when the
tetrahydrofuran-soluble components of the toner at 25° C. are
subjected to measurement by SEC-MALLS, the weight-average molecular
weight Mw be 5,000 or more and 100,000 or less, preferably 5,000 or more
and 25,000 or less. That the weight-average molecular weight Mw is
100,000 or less means that the binder resin in the toner has a low
molecular weight, and the combination of the resin with a specific
release agent enables easy fixation even in a light-pressure type fixing
unit construction. In addition, when the weight-average molecular weight
Mw is 5,000 or more, the elasticity of the toner is maintained upon
charging of the toner, and hence the toner is easily charged in a uniform
fashion. In addition, an image density and image quality can be held at
the time of its long-term use. When the weight-average molecular weight
Mw is larger than 100,000, the toner hardly plasticizes, and hence its
fixability deteriorates. In addition, the dispersibility of the release
agent (a) is apt to reduce, and hence the fixation is apt to be further
difficult. On the other hand, when the weight-average molecular weight Mw
is smaller than 5,000, the elasticity of the toner is apt to reduce upon
charging of the toner, and hence the charging is apt to be nonuniform. In
addition, the toner is apt to be deformed at the time of its long-term
use, and hence reductions in density and image quality are apt to occur.

[0068] Next, that the ratio Rw/Mw between the weight-average molecular
weight Mw and radius of gyration Rw of the tetrahydrofuran-soluble
components of the toner at 25° C. is 5.0×10-4 or more
and 1.0×10-2 or less means that the binder resin in the toner
has a linear type molecular structure. Accordingly, the dispersibility of
each of the materials such as the release agent (a) in the toner is
improved, and hence the fixability and the image quality at the time of
the long-term use are easily improved.

[0069] In addition, an interaction between the binder resin and the
release agent (a) strengthens. As a result, the storage stability of the
toner under a high-temperature, high-humidity environment is improved,
and the toner can maintain good developability even after having been
left to stand under the high-temperature, high-humidity environment.

[0070] That the Rw/Mw is smaller than 5.0×10-4 means that the
binder resin has a branched type molecular structure. Accordingly, the
dispersibility of each of the materials in the toner, in particular the
monofunctional or bifunctional ester wax reduces. When the Rw/Mw is
larger than 1.0×10-2, it becomes difficult to produce the
toner stably and image density unevenness is apt to occur at the time of
the long-term use of the resultant toner.

[0071] It should be noted that the Rw/Mw is more preferably
2.0×10-3 or more and 1.0×10-2 or less. When the
Rw/Mw falls within the range, the fixability, and the density and image
quality at the time of the long-term use are further easily improved.

[0072] The radius of gyration Rw is preferably 20 or more and 70 or less.
When the radius of gyration is 20 or more and 70 or less, the molecular
weight of the binder resin is small, and hence its extent of branching is
easily controlled.

[0073] In addition, when the tetrahydrofuran-soluble components of the
toner at 25° C. are subjected to measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS), their
number-average molecular weight Mn(25° C.) is preferably 500 or
more and 3,000 or less, and the number-average molecular weight Mn is
more preferably 1,000 or more and 2,500 or less. When the toner satisfies
the requirement, the deformation of the toner can be properly controlled,
and hence its low-temperature fixability is improved. In addition, its
charging stability at the time of its long-term use becomes high, and
hence the dot reproducibility is easily improved. Further, the storage
stability is also improved.

[0074] In addition, in the present invention, even when the ratio
(Mn(135° C.)/Mn(25° C.)) between the number-average
molecular weight Mn(25° C.) when the tetrahydrofuran-soluble
components of the toner at 25° C. are subjected to measurement by
size exclusion chromatography-multiangle laser light scattering
(SEC-MALLS) and the number-average molecular weight Mn(135° C.)
when the o-dichlorobenzene-soluble components of the toner at 135°
C. are subjected to measurement by size exclusion
chromatography-multiangle laser light scattering (SEC-MALLS) is less than
25, an effect of the present invention can be obtained.

[0075] The weight-average molecular weight Mw, and the ratio Rw/Mw between
the weight-average molecular weight Mw and the radius of gyration Rw can
be adjusted by changing the kind and amount of a polymerization
initiator, and a reaction condition as described later.

[0076] In addition, it is preferred that heat of fixation uniformly
propagate through the toner in order that good fixation be realized in a
light-pressure type fixing unit construction. To that end, the shape of
the toner is preferably spherical. When the shape is spherical, the toner
on paper is brought close to a close-packed one, and hence heat
efficiency is easily improved.

[0077] In view of the foregoing, the toner preferably has an average
circularity of 0.960 or more. When the average circularity of the toner
is 0.960 or more, its thermal conductivity becomes uniform, and hence
low-temperature fixation can be performed. As a result, density
uniformity and the dot reproducibility are easily improved. Further, when
the average circularity increases, the shear applied to the toner upon
development easily becomes uniform, and hence the toner easily realizes a
uniform density and high image quality over a long time period. In
addition, even after the toner has been left to stand under a
high-temperature, high-humidity environment, the toner has good
flowability and good chargeability, and hence easily obtains good
developability.

[0078] Next, an improvement in the flowability of the toner particles
themselves is effective in reducing a change in the state of the surface
of each of the toner particles at the time of their long-term use due to,
for example, the embedment of an external additive. A total energy
measured with a powder flowability analyzer when the agitation rate is
100 mm/sec is given as an indicator of the flowability of the toner
particles.

[0079] The toner of the present invention is preferably such that the
total energy of the toner particles measured with a powder flowability
analyzer when the agitation rate is 100 mm/sec is 500 mJ or more and
1,000 mJ or less. A total energy of 500 mJ or more is preferred because
the triboelectric chargeability of the toner is easily improved.
Meanwhile, a total energy of 1,000 mJ or less is preferred because the
flowability is improved. When the total energy is 500 mJ or more and
1,000 mJ or less, a balance can be established between the triboelectric
chargeability and the flowability by such reasons. Accordingly, the toner
easily holds a high image density and high image quality even upon
embedment of, for example, an external additive at the time of its
long-term use. Therefore, such total energy is preferred.

[0080] Providing the surface of each toner particle with a strong outer
shell is effective in enhancing the flowability of such toner particles
themselves and improving their storage stability. The presence of the
outer shell increases the hardness of each particle, thereby enhancing
the flowability. In addition, the presence of the outer shell can
suppress the embedment of an external additive, and hence an improvement
in the stress resistance of the toner and reductions in the variations of
the characteristics of the toner at the time of its long-term use can be
realized.

[0081] In addition, it has been important for the outer shell to suppress
a variation in covered state among toner particles and to uniformly cover
each particle so that the exposure of the binder resin be prevented. In
the case where the toner is produced by, for example, a wet process,
simply mixing a material serving as the outer shell to form the toner
particles or simply adding the outer shell material after the formation
of a core does not suffice for the formation of such outer shell, and a
correlation with the binder resin needs to be controlled. In other words,
the outer shell material does not uniformly cover the toner surface or
the outer shell does not have a moderate thickness until the
weight-average molecular weight Mw and the radius of gyration Rw are
adjusted, and the kind and amount of the outer shell agent are
controlled. Accordingly, a uniform, strong outer shell can be formed by
such adjustment and control. As a result of the formation, the toner
characteristics that satisfy the present invention can be exhibited. That
is, an image having a high image density and high dot reproducibility can
be obtained over a long time period. In addition, the low-temperature
fixability can be improved.

[0082] The kind of such outer shell agent is preferably a polyester resin,
particularly preferably a polyester obtained by polycondensation with a
titanium-based catalyst. The polyester obtained by polycondensation with
a titanium-based catalyst is preferred because the polyester easily
becomes homogeneous and hence easily covers the surface of each toner
particle in a uniform fashion.

[0083] In addition, when the homogeneous polyester, and the binder resin
having a low molecular weight and a linear type molecular structure of
the present invention are combined with each other, upon formation of the
toner particles in a low-viscosity state such as a polymerizable monomer
like, for example, suspension polymerization, sufficient molecular motion
is possible, and hence the outer shell covers the surface more uniformly.

[0084] The content of the polyester resin is preferably 7 parts by mass or
more and 30 parts by mass or less with respect to 100 parts by mass of
the binder resin. When the content of the polyester resin is 7 parts by
mass or more, the flowability of the toner particles is easily improved.
In addition, when the content of the polyester resin is 30 parts by mass
or less, the dispersibility of a release agent, a coloring agent, or the
like is easily improved, and hence the low-temperature fixability is
improved.

[0085] Next, the binder resin of the present invention preferably uses, as
a main component, a resin obtained by polymerization with a
peroxydicarbonate as a polymerization initiator. When the binder resin is
produced by, for example, radical polymerization, the use of the
peroxydicarbonate as the polymerization initiator results in the
production of two carbonate radicals of the same kind upon its cleavage.
In addition, a carbonate radical hardly causes a decarboxylation
reaction. As a result, radicals of the same kind easily exist in a
reaction system, and hence the radical polymerization of a polymerizable
monomer can be efficiently initiated. Accordingly, the molecular weight
of the binder resin can be reduced by using the initiator in a smaller
amount than that of a conventional peroxide type polymerization
initiator. Further, the case where the molecular weight can be reduced by
using the initiator in the smaller amount is preferred because a side
reaction and the like hardly occur and hence a linear type molecular
structure is easily produced.

[0086] When the binder resin of the present invention is produced by
radical polymerization, the polymerization initiator is preferably used
at a temperature higher than its 10-hour halflife temperature by
15° C. or more. When the polymerization initiator is used at a
temperature higher than its 10-hour halflife temperature by 15° C.
or more, the cleavage of the polymerization initiator becomes rapid, and
hence the reduction in the molecular weight is easily attained. In
addition, radicals of the same kind are easily produced in the reaction
system, and hence a side reaction hardly occurs. Accordingly, a binder
resin having a linear type molecular structure is easily produced.

[0087] With regard to a method of adding the polymerization initiator, the
polymerization initiator can be added collectively or dividedly.

[0088] Examples of the binder resin to be used in the toner of the present
invention include: homopolymers of styrene and substituted derivatives
thereof, such as polystyrene and polyvinyl toluene; styrene-based
copolymers such as a styrene-propylene copolymer, a styrene-vinyl toluene
copolymer, a styrene-vinyl naphthalene copolymer, a styrene-methyl
acrylate copolymer, a styrene-ethyl acrylate copolymer, a styrene-butyl
acrylate copolymer, a styrene-octyl acrylate copolymer, a
styrene-dimethylaminoethyl acrylate copolymer, a styrene-methyl
methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a
styrene-butyl methacrylate copolymer, a styrene-dimethylaminoethyl
methacrylate copolymer, a styrene-vinyl methyl ether copolymer, a
styrene-vinyl ethyl ether copolymer, a styrene-vinyl methyl ketone
copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a
styrene-maleic acid copolymer, and a styrene-maleic acid ester copolymer;
and polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate,
polyethylene, polypropylene, polyvinylbutyral, a silicone resin, a
polyester resin, a polyamide resin, an epoxy resin, and a polyacrylic
acid resin. Those may be used alone or in combination of multiple kinds
thereof. Of those, a styrene-based copolymer using styrene as a main
component is particularly preferred in terms of, for example, developing
characteristic and fixability, and a styrene-alkyl acrylate-based
copolymer or a styrene-alkyl methacrylate-based copolymer is more
preferably used as a main component. When any such copolymer is used, the
binder resin is easily provided with a linear type molecular structure,
and the states of presence of the release agent (a) and the release agent
(b) are easily made suitable.

[0089] In the toner of the present invention, in order to improve the
charging characteristics, a charge control agent may be blended as
required. A known agent can be utilized as the charge control agent, and
a charge control agent that can quickly cause charging and can stably
maintain a certain charge quantity is particularly preferred. Further,
when the toner is produced by a polymerization method as described later,
a charge control agent which has low polymerization-inhibiting property
and is substantially free of any soluble matter in the aqueous medium is
particularly preferred. Specific compounds as negative-type charge
control agents out of the charge control agents can be exemplified by
metal compounds of aromatic carboxylic acids such as salicylic acid, an
alkylsalicylic acid, a dialkylsalicylic acid, naphthoic acid, and
dicarboxylic acids; metal salts and metal complexes of azo dyes and azo
pigments; polymer compounds each having a sulfonic acid group or
carboxylic acid group in a side chain position; boron compounds; urea
compounds; silicon compounds; and calixarenes. Positive-type charge
control agents can be exemplified by quaternary ammonium salts, polymer
compounds each having any of the quaternary ammonium salts in a side
chain position, guanidine compounds, nigrosin-based compounds, and
imidazole compounds.

[0090] Generally employed as a method of incorporating the charge control
agent into the toner is a method involving adding the charge control
agent to the inside of each toner particle or, when the toner is produced
by suspension polymerization, a method involving adding the charge
control agent into a polymerizable monomer composition before
granulation. Alternatively, the surface of the toner can be uniformly
covered by performing seed polymerization as described below. A
polymerizable monomer in which the charge control agent is dissolved or
suspended is added during the performance of polymerization through the
formation of an oil droplet in water or after the polymerization.
Alternatively, when an organometallic compound is used as the charge
control agent, such compound can be introduced by adding the compound to
each toner particle and applying a shear to mix and agitate the contents.

[0091] The usage of such charge control agent is determined by the kind of
the binder resin, the presence or absence of any other additive, and the
production method for the toner including a dispersion method, and is
hence not uniquely limited. However, when the charge control agent is
internally added to each toner particle, the charge control agent is used
in an amount in the range of preferably 0.1 part by mass or more and 10
parts by mass or less, more preferably 0.1 part by mass or more and 5
parts by mass or less with respect to 100 parts by mass of the binder
resin. In addition, when the charge control agent is externally added to
each toner particle, the amount is preferably 0.005 part by mass or more
and 1.0 part by mass or less, more preferably 0.01 part by mass or more
and 0.3 part by mass or less with respect to 100 parts by mass of the
toner.

[0092] The toner of the present invention contains a coloring agent suited
for a target tint. A known organic pigment or dye, carbon black, a
magnetic substance, and the like can each be used as the coloring agent
to be used in the toner of the present invention.

[0096] Those coloring agents may be used alone, or as a mixture or solid
solution of two or more kinds thereof. The coloring agent used in the
toner of the present invention is appropriately selected in view of hue
angle, chroma, saturation, brightness, lightfastness, OHP transmissivity,
and dispersibility in toner. In addition, the addition amount of the
coloring agent is preferably 1 part by mass or more and 20 parts by mass
or less with respect to 100 parts by mass of the binder resin.

[0097] Further, there are utilized, as black coloring agents, carbon
black, a magnetic substance, and one toned to black by using the
above-mentioned yellow/magenta/cyan coloring agents. When the carbon
black is used as a black coloring agent, its addition amount is
preferably 1 part by mass or more and 20 parts by mass or less with
respect to 100 parts by mass of the binder resin.

[0098] In addition, when the toner of the present invention is used as a
magnetic toner, a magnetic substance can also be used as the coloring
agent. When a magnetic substance is used as a black coloring agent, the
addition amount of the magnetic substance is preferably 20 parts by mass
or more and 150 parts by mass or less with respect to 100 parts by mass
of the binder resin.

[0099] When the addition amount of the magnetic substance is 20 parts by
mass or more, the toner has high coloring power and fogging is easily
suppressed. In addition, when the addition amount is 150 parts by mass or
less, the endotherm of the magnetic substance reduces, and hence the
fixability is more likely to be improved.

[0100] It should be noted that the content of the magnetic substance in
the toner can be measured with a thermal analyzer TGA7 manufactured by
PerkinElmer Co., Ltd. A method for the measurement is as described below.
Under a nitrogen atmosphere, the toner is heated from normal temperature
to 900° C. at a heating rate of 25° C./min. The loss (mass
%) in the range of 100° C. to 750° C. is defined as the
amount of the binder resin, and the remaining mass is approximately
defined as the amount of the magnetic substance.

[0101] When the toner is produced by employing a polymerization method in
the present invention, attention should be paid to the
polymerization-inhibiting property and aqueous phase-migrating property
of the coloring agent. In view of the foregoing, the coloring agent is
desirably subjected to surface modification such as a hydrophobic
treatment with a substance that does not inhibit any polymerization.
Particular attention should be paid to dyes and carbon black upon their
use because many of the dyes and the carbon black have
polymerization-inhibiting properties.

[0102] The carbon black may be treated with a substance that reacts with a
surface functional group of the carbon black such as polyorganosiloxane.

[0103] When the magnetic substance is used in the toner of the present
invention, the magnetic substance uses a magnetic iron oxide such as
triiron tetroxide or γ-iron oxide as a main component, and may
contain an element such as phosphorus, cobalt, nickel, copper, magnesium,
manganese, aluminum, or silicon. Any such magnetic substance has a BET
specific surface area by nitrogen adsorption of preferably 2 m2/g or
more and 30 m2/g or less, more preferably 3 m2/g or more and 28
m2/g or less. Further, the magnetic substance preferably has a Mohs
hardness of 5 or more and 7 or less. Examples of the shape of the
magnetic substance include a polyhedral shape, an octahedral shape, a
hexahedral shape, a spherical shape, a needle shape, and a scaly shape.
The magnetic substance preferably has a shape with a low degree of
anisotropy, such as a polyhedral shape, an octahedral shape, a hexahedral
shape, or a spherical shape in order to increase image density.

[0104] The magnetic substance preferably has a volume-average particle
diameter (Dv) of 0.10 μm or more and 0.40 μm or less. When the
volume-average particle diameter (Dv) is 0.10 μm or more, the
particles of the magnetic substance hardly agglomerate, and hence the
uniform dispersibility of the magnetic substance in the toner is
improved. In addition, the magnetic substance having a volume-average
particle diameter (Dv) of 0.40 μm or less is preferably used because
the coloring power of the toner is improved.

[0105] It should be noted that the volume-average particle diameter (Dv)
of the magnetic substance can be measured with a transmission electron
microscope. Specifically, the toner particles to be observed are
sufficiently dispersed in an epoxy resin, and then the resultant is cured
in an atmosphere having a temperature of 40° C. for 2 days so that
a cured product be obtained. The resultant cured product is turned into a
flaky sample with a microtome, and then the sample is photographed with a
transmission electron microscope (TEM) at a magnification of 10,000 to
40,000. The diameters of 100 magnetic substance particles in the field of
view of the photograph are measured. Then, the volume-average particle
diameter (Dv) is calculated on the basis of the equivalent diameter of a
circle equal in area to the projected area of the magnetic substance.
Alternatively, the particle diameters can be measured with an image
analyzer.

[0106] The magnetic substance to be used in the toner of the present
invention can be produced by, for example, the following method. An
alkali such as sodium hydroxide is added to an aqueous solution of a
ferrous salt in an equivalent or more with respect to the iron component
so that an aqueous solution containing ferrous hydroxide be prepared.
While the pH of the prepared aqueous solution is maintained at 7 or more,
air is blown into the aqueous solution. Then, the oxidation reaction of
ferrous hydroxide is performed while the aqueous solution is heated to
70° C. or more. Thus, a seed crystal serving as the core of a
magnetic iron oxide powder is produced first.

[0107] Next, an aqueous solution containing about one equivalent of
ferrous sulfate with reference to the addition amount of the alkali
previously added is added to the slurry liquid containing the seed
crystal. While the pH of the resultant liquid is maintained at 5 to 10,
air is blown into the liquid. During the blowing, the reaction of ferrous
hydroxide is advanced so that the magnetic iron oxide powder be grown
with the seed crystal as a core. At this time, the shape and magnetic
characteristics of the magnetic substance can be controlled by selecting
an arbitrary pH, an arbitrary reaction temperature, and an arbitrary
agitation condition. As the oxidation reaction progresses, the pH of the
liquid shifts to acidic values. However, the pH of the liquid is
preferably prevented from becoming less than 5. The magnetic substance
thus obtained is filtrated, washed, and dried by ordinary methods. Thus,
the magnetic substance can be obtained.

[0108] In addition, when the toner is produced by a polymerization method
in the present invention, the surface of the magnetic substance is
extremely preferably subjected to a hydrophobic treatment. When the
surface is treated by a dry process, the magnetic substance that has been
washed, filtrated, and dried is treated with a coupling agent. When the
surface is treated by a wet process, the dried product after the
termination of the oxidation reaction is re-dispersed, or the iron oxide
body obtained by the washing and filtration after the termination of the
oxidation reaction is re-dispersed in another aqueous medium without
being dried, followed by a coupling treatment. Specifically, the coupling
treatment is performed by adding a silane coupling agent while
sufficiently agitating the re-dispersion liquid, and hydrolyzing the
agent and then increasing the temperature of the re-dispersion liquid or
hydrolyzing the agent and then adjusting the pH of the dispersion liquid
to an alkali region. The surface treatment is preferably performed by the
following method out of such methods as described above from such a
viewpoint that the surface treatment is uniformly performed. After the
termination of the oxidation reaction, the resultant is filtrated and
washed, and is then directly turned into slurry without being dried.

[0109] In order that the surface treatment of the magnetic substance be
performed by the wet process, that is, the magnetic substance be treated
with a coupling agent in an aqueous medium, first, the magnetic substance
is sufficiently dispersed in the aqueous medium so as to have a primary
particle diameter, and then the dispersion liquid is agitated with an
agitation blade or the like lest the particles of the magnetic substance
should precipitate or agglomerate. Next, an arbitrary amount of the
coupling agent is added into the above-mentioned dispersion liquid, and
then the surface treatment is performed while the coupling agent is
hydrolyzed. At this time as well, it is more preferred that the surface
treatment be performed while the magnetic substance is sufficiently
dispersed with an apparatus such as a pin mill or a line mill lest the
agglomeration should occur during the performance of the agitation.

[0110] The term "aqueous medium" as used herein refers to a medium mainly
formed of water. Specific examples thereof include water itself, a medium
obtained by adding a small amount of a surfactant to water, a medium
obtained by adding a pH adjustor to water, and a medium obtained by
adding an organic solvent to water. A nonionic surfactant such as
polyvinyl alcohol is preferably used as the surfactant. The surfactant is
preferably added in an amount of 0.1 to 5.0 mass % with respect to water.
Examples of the pH adjustor include inorganic acids such as hydrochloric
acid. Examples of the organic solvent include alcohols.

[0111] As a coupling agent that can be used for a surface treatment of the
magnetic substance in the present invention, a silane coupling agent and
a titanium coupling agent are given, for example. Of those, more
preferably used is a silane coupling agent which is represented by the
general formula (1).

RmSiYn general formula (1)

(In the formula, R represents an alkoxy group, m represents an integer of
1 to 3, Y represents a functional group such as an alkyl group, a vinyl
group, an epoxy group, an acrylic group, or a methacrylic group, and n
represents an integer of 1 to 3, provided that m+n=4.)

[0113] Of those, an alkyltrialkoxysilane coupling agent represented by the
following general formula (2) is preferably used from such a viewpoint
that high hydrophobicity is imparted to the magnetic substance.

CpH2p+1--Si--(OCqH2q+1)3 General formula (2)

(In the formula, p represents an integer of 2 to 20 and q represents an
integer of 1 to 3.)

[0114] It is preferred to use an alkyltrialkoxysilane coupling agent
represented by the above-mentioned formula, where p represents an integer
of 2 to 20 (more preferably an integer of 3 to 15) and q represents an
integer of 1 to 3 (more preferably an integer of 1 or 2).

[0115] When the above-mentioned silane coupling agent is used, the
magnetic substance can be treated with one kind of such agent alone, or
can be treated with multiple kinds thereof in combination. When multiple
kinds thereof are used in combination, the magnetic substance may be
treated with each of the coupling agents individually, or may be treated
with the agents simultaneously.

[0116] The total treatment amount of the coupling agent to be used is
preferably 0.9 part by mass or more and 3.0 parts by mass or less with
respect to 100 parts by mass of the magnetic substance, and it is
important that the amount of the treatment agent be adjusted depending
on, for example, the surface area of the magnetic substance and the
reactivity of the coupling agent.

[0117] In the present invention, a coloring agent other than the magnetic
substance may be used together. Examples of the coloring agent that can
be used together include, in addition to the above-mentioned known dyes
and pigments, magnetic or non-magnetic inorganic compounds. Specific
examples thereof include ferromagnetic metal particles such as cobalt and
nickel, alloys thereof obtained by adding chromium, manganese, copper,
zinc, aluminum, rare-earth elements, and the like thereto, particles such
as hematite, titanium black and nigrosine dyes/pigments, carbon black,
and phthalocyanine. Those are also preferably used after being subjected
to a surface treatment.

[0118] The toner preferably has a weight-average particle diameter (D4) of
5.0 μm or more and 9.0 μm or less in order that sufficient image
characteristics be obtained. When the weight-average particle diameter
(D4) is 5.0 μm or more, regulation with a developing blade easily
becomes sufficient, and hence the toner is easily uniformly charged. In
addition, when the weight-average particle diameter (D4) is 9.0 μm or
less, dot reproducibility is easily improved, and hence a high-definition
image is easily obtained.

[0119] The toner of the present invention preferably has a glass
transition temperature (Tg) of 40° C. or more and 70° C. or
less. When the glass transition temperature is 40° C. or more, the
storage stability is improved and the toner hardly deteriorates even
after its long-term use. In addition, when the glass transition
temperature is 70° C. or less, the fixability is improved.
Accordingly, the glass transition temperature of the toner is preferably
40° C. or more and 70° C. or less in consideration of a
balance among its fixability, storage stability, and developability.

[0120] The toner of the present invention preferably has a core-shell
structure for improving its image stability at the time of its long-term
use. This is because the presence of a shell layer (outer shell)
uniformizes the surface property of the toner, improves the flowability,
and uniformizes the chargeability.

[0121] In addition, the shell as a high-molecular weight body uniformly
covers the surface layer, and hence the exudation of the release agents
and the like hardly occur even after long-term storage of the toner and
the storage stability is improved.

[0122] Accordingly, an amorphous high-molecular weight body is preferably
used in the shell layer, and its acid value is preferably 1.0 mgKOH/g or
more and 20.0 mgKOH/g or less from the viewpoint of charging stability.
When the acid value of the high-molecular weight body to be used in the
shell layer is 20.0 mgKOH/g or less, the chargeability of the toner is
easily stabilized, and hence its developability particularly under a
high-temperature, high-humidity environment is improved. In addition,
when the acid value of the high-molecular weight body to be used in the
shell layer is 1.0 mgKOH/g or more, a robust shell is easily formed, and
hence the storage stability is additionally improved.

[0123] With regard to a specific approach for forming the shell, the shell
layer can be formed by embedding fine particles for the shell in core
particles or, when the toner is produced in an aqueous medium according
to the production method suitable for the present invention, causing
ultra-fine particles for the shell to adhere to the core particles and
drying the resultant. In addition, in a dissolution suspension method or
the suspension polymerization method, the shell can be formed by causing
the high-molecular weight body for the shell to be unevenly distributed
at an interface with water, i.e., in the vicinity of the surface of the
toner by means of the acid value and hydrophilicity of such
high-molecular weight body. Further, the shell can be formed by swelling
a monomer on the surface of each core particle and polymerizing the
monomer by the so-called seed polymerization method.

[0124] Examples of the high-molecular weight body for the shell layer
include: homopolymers of styrene and substituted derivatives thereof,
such as polystyrene and polyvinyl toluene; styrene-based copolymers such
as a styrene-propylene copolymer, a styrene-vinyl toluene copolymer, a
styrene-vinyl naphthalene copolymer, a styrene-methyl acrylate copolymer,
a styrene-ethyl acrylate copolymer, a styrene-butyl acrylate copolymer, a
styrene-octyl acrylate copolymer, a styrene-dimethylaminoethyl acrylate
copolymer, a styrene-methyl methacrylate copolymer, a styrene-ethyl
methacrylate copolymer, a styrene-butyl methacrylate copolymer, a
styrene-dimethylaminoethyl methacrylate copolymer, a styrene-vinyl methyl
ether copolymer, a styrene-vinyl ethyl ether copolymer, a styrene-vinyl
methyl ketone copolymer, a styrene-butadiene copolymer, a
styrene-isoprene copolymer, a styrene-maleic acid copolymer, and a
styrene-maleic acid ester copolymer; and polymethyl methacrylate,
polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene,
polyvinylbutyral, a silicone resin, a polyester resin, a
styrene-polyester copolymer, a polyacrylate-polyester copolymer, a
polymethacrylate-polyester copolymer, a polyamide resin, an epoxy resin,
a polyacrylic acid resin, a terpene resin, and a phenol resin. Those may
be used alone or as a mixture of two or more kinds thereof. Further, a
functional group may be introduced into any such polymer, such as an
amino group, a carboxyl group, a hydroxyl group, a sulfonic acid group, a
glycidyl group, or a nitrile group.

[0125] Of those resins, a polyester is preferred as described in the
foregoing.

[0126] One or both of a saturated polyester resin and an unsaturated
polyester resin which are appropriately selected can be used as the
polyester resin to be used in the present invention.

[0127] An ordinary resin formed of an alcohol component and an acid
component can be used as the polyester resin to be used in the present
invention, and examples of both the components are given below.

(in the formula, R represents an ethylene or propylene group, x and y
each represent an integer of 1 or more, and the average of x+y is 2 to
10) or a hydrogenated product of the compound represented by the formula
(I), and a diol represented by the formula (II):

##STR00002##

(in the formula, R' represents --CH2CH2--,
--CH2--CH(CH3)--, or --CH2--C(CH3)2--) or a diol
of a hydrogenated product of the compound represented by the formula
(II).

[0129] As a divalent carboxylic acid, there are given: benzenedicarboxylic
acids and anhydrides thereof, such as phthalic acid, terephthalic acid,
isophthalic acid, and phthalic anhydride; alkyldicarboxylic acids and
anhydrides thereof, such as succinic acid, adipic acid, sebacic acid, and
azelaic acid; succinic acid substituted with an alkyl or alkenyl group
having 6 to 18 carbon atoms and an anhydride thereof; and unsaturated
dicarboxylic acids and anhydrides thereof, such as fumaric acid, maleic
acid, citraconic acid, and itaconic acid; and the like.

[0130] Further examples of the alcohol component include polyhydric
alcohols such as glycerin, pentaerythritol, sorbit, sorbitan, and an
oxyalkylene ether of a novolak type phenol resin. Further examples of the
acid component include polyvalent carboxylic acids such as trimellitic
acid, pyromellitic acid, 1,2,3,4-butanetetracarboxylic acid, and
benzophenonetetracarboxylic acid, and anhydrides thereof.

[0131] Of the above-mentioned polyester resins, the alkylene oxide adduct
of bisphenol A which is excellent in charging characteristic and
environmental stability, and other electrophotographic characteristics of
which are balanced is preferably used. In the case of such compound, the
average number of moles of the added alkylene oxide is preferably 2 or
more and 10 or less in terms of the fixability and the durability of the
toner.

[0132] It is preferred that the alcohol component account for 45 mol % or
more and 55 mol % or less of all components of the polyester resin in the
present invention, and the acid component account for 45 mol % or more
and 55 mol % or less thereof.

[0133] Although the polyester resin in the present invention can be
produced with any one of the catalysts such as a tin-based catalyst, an
antimony-based catalyst, and a titanium-based catalyst, the
titanium-based catalyst is preferably used as described in the foregoing.

[0134] In addition, a high-molecular weight body having a number-average
molecular weight of 2,500 or more and 25,000 or less is preferably used
as the high-molecular weight body that forms the shell. When the
number-average molecular weight is 2,500 or more, the developability,
blocking resistance, and durability of the toner are improved. In
addition, a number-average molecular weight of 25,000 or less is
preferred because the low-temperature fixability is improved. It should
be noted that the number-average molecular weight can be measured by GPC.

[0135] Next, specific examples of the monofunctional or bifunctional ester
include: waxes each having a fatty acid ester as a main component, such
as a carnauba wax and a montanic acid ester wax; and those obtained by
subjecting part or the whole of the acid components of fatty acid esters
to deacidification, such as a deacidified carnauba wax; methyl ester
compounds each having a hydroxyl group obtained by hydrogenation of
vegetable fats and oils; saturated fatty acid monoesters such as stearyl
stearate and behenyl behenate; diesterfied products of saturated
aliphatic dicarboxylic acids and saturated aliphatic alcohols, such as
dibehenyl sebacate, distearyl decanedioate, and distearyl
octadecanedioate; and diesterfied products of saturated aliphatic diols
and saturated fatty acids, such as nonanediol dibehenate and dodecanediol
distearate.

[0137] The release agent (a) can be used in an amount in the range of 5
parts by mass or more and 20 parts by mass or less with respect to 100
parts by mass of the binder resin. When the amount falls within the range
of 5 parts by mass or more and 20 parts by mass or less, the
dispersibility in the binder resin is improved, and hence the fixability
and development stability at the time of the long-term use are improved.

[0138] Next, as a hydrocarbon wax, there may be used, specifically:
aliphatic hydrocarbon-based waxes such as low-molecular weight
polyethylene, low-molecular weight polypropylene, a microcrystalline wax,
a paraffin wax, and a Fischer-Tropsch wax; oxides of aliphatic
hydrocarbon-based waxes such as a polyethylene oxide wax or block
copolymers thereof; and waxes obtained by grafting aliphatic
hydrocarbon-based waxes with vinyl-based monomers such as styrene and
acrylic acid, for example. Of those, a paraffin wax or a Fischer-Tropsch
wax is preferably used in the range of 0.1 part by mass or more and 20
parts by mass or less with respect to 100 parts by mass of the binder
resin.

[0139] The release agent (a) and the release agent (b) each preferably
have a maximum endothermic peak in a region of 60° C. or more and
85° C. or less during heating in a DSC curve measured with a
differential scanning calorimeter. The presence of the maximum
endothermic peak in the above-mentioned temperature region improves the
low-temperature fixability and the development stability. In addition,
upon production of the toner particles by the suspension polymerization
method as a method of producing toner particles suitable for the present
invention, the dispersed state of each release agent is easily controlled
to a desired one because its solubility in a polymerizable monomer is
improved.

[0141] The toner of the present invention is a toner comprising toner
particles, each of which contains the binder resin, the coloring agent,
the release agent (a), and the release agent (b), and can be produced by
any one of the known methods. First, when the toner is produced by a
pulverization method, components needed for the toner such as the binder
resin, the coloring agent, the release agent (a), the release agent (b),
and the charge control agent, any other additive, and the like are
sufficiently mixed with a mixer such as a Henschel mixer or a ball mill.
After that, the mixture is melted and kneaded with a heat kneader such as
a heat roll, a kneader, or an extruder so that the toner materials may be
dispersed or dissolved. Then, the resultant is cooled to solidify and
pulverized. After that, the pulverized products are classified, and as
required, subjected to a surface treatment. Thus, the toner particles can
be obtained. The dispersed states of the release agent (a) and the
release agent (b) in the binder resin can be adjusted by controlling
temperature and kneading conditions at the time of the melt kneading. In
addition, it does not matter which one of the classification and the
surface treatment is performed prior to the other. In the classifying
step, a multi-division classifier is preferably used in terms of
production efficiency.

[0142] The pulverizing step can be performed by a method involving using a
known pulverizing apparatus such as a mechanical impact type or jet type
pulverizing apparatus. In addition, in order that the toner having a
preferred circularity of the present invention be obtained, it is
preferred that the pulverized products be further pulverized by applying
heat or a treatment involving additionally applying a mechanical impact
in an auxiliary fashion be performed. Alternatively, a hot water bath
method involving dispersing finely pulverized toner particles (classified
as required) in hot water, a method involving passing the particles
through a heat air current, or the like may be employed.

[0143] For example, a method involving using a mechanical impact type
pulverizer such as a Kryptron system manufactured by Kawasaki Heavy
Industries Co. or a Turbo mill manufactured by Turbo Kogyo Co., Ltd. is
given as means for applying a mechanical impact force. Also given is a
method involving pressing the toner against the inside of a casing with a
blade rotating at a high speed by means of a centrifugal force and
applying a mechanical impact force to the toner by means of a force such
as a compressive force or a frictional force like an apparatus such as a
Mechanofusion System manufactured by Hosokawa Micron Corporation or a
Hybridization System manufactured by NARA MACHINERY CO., LTD. A
Meteorainbow (manufactured by Nippon Pneumatic Mfg. Co., Ltd.) is given
as means for passing the particles through a heat air current.

[0144] Although the toner of the present invention can be produced by the
pulverization method as described above, the toner particles obtained by
the pulverization method are generally amorphous. Accordingly, a
mechanical or thermal treatment, or any special treatment needs to be
performed for obtaining the uniform chargeability of the present
invention, and hence productivity deteriorates. In view of the foregoing,
the toner of the present invention is preferably produced in an aqueous
medium like, for example, a dispersion polymerization method, an
association agglomeration method, a dissolution suspension method, or a
suspension polymerization method. When the toner is produced in the
aqueous medium, the binder resin as a feature of the present invention is
optimized. Further, the selection of a suitable release agent enables one
to easily obtain a toner with its structure highly controlled.

[0145] In particular, in the suspension polymerization method, the toner
is produced from a polymerizable monomer. Accordingly, a liquid viscosity
at an initial stage of the production is easily reduced, and hence the
states of presence of the coloring agent and the release agents are
easily adjusted. Further, the shapes of the toner particles are easily
uniformized, and hence physical properties suitable for the present
invention are easily satisfied. For example, uniform charging of the
toner is easily attained or heat is easily applied to the toner in a
uniform fashion at the time of fixation. Accordingly, the method is
extremely preferred.

[0146] The suspension polymerization method involves: uniformly dissolving
or dispersing the polymerizable monomer and the coloring agent (and a
polymerization initiator, a crosslinking agent, the charge control agent,
and any other additive as required) to provide a polymerizable monomer
composition; and dispersing the polymerizable monomer composition in a
continuous layer (such as an aqueous phase) containing a dispersion
stabilizer with a proper agitator and performing a polymerization
reaction simultaneously with the dispersion to provide a toner having a
desired particle diameter. The toner obtained by the suspension
polymerization method (which may hereinafter be referred to as
"polymerized toner") is such that the shapes of individual toner
particles are uniformized so as to be substantially spherical.
Accordingly, a toner that satisfies physical property requirements
suitable for the present invention such as the uniform chargeability and
the dispersibility of the coloring agent is easily obtained.

[0147] In the production of the polymerized toner according to the present
invention, examples of the polymerizable monomer that constructs the
polymerizable monomer composition include the following monomers.

[0148] Examples of the polymerizable monomer include: styrene-based
monomers such as styrene, o-methylstyrene, m-methylstyrene,
p-methylstyrene, p-methoxystyrene, and p-ethylstyrene; acrylates such as
methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl
acrylate, stearyl acrylate, 2-chloroethyl acrylate, and phenyl acrylate;
methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl
methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl
methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl
methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, and
diethylaminoethyl methacrylate; and other monomers such as acrylonitrile,
methacrylonitrile, and acrylamide. Those monomers may be used alone or in
admixture with each other. Of the above-mentioned monomers, the use of
styrene or a styrene derivative alone or in admixture with any other
monomer is preferred in terms of ease of controlling the toner structure
and ease of improving the developing performance and durability of the
toner. In particular, the use of styrene and an alkyl acrylate, or
styrene and an alkyl methacrylate as main components is more preferred.

[0149] The polymerization initiator to be used in the production of the
toner of the present invention by a polymerization method preferably has
a half-life of 0.5 hour or more and 30 hours or less in a polymerization
reaction. Further, when the polymerization reaction is conducted with the
polymerization initiator added in an amount of 0.5 part by mass or more
and 20 parts by mass or less with respect to 100 parts by mass of the
polymerizable monomer, a polymer having the maximum molecular weight in
the range of 5,000 or more and 50,000 or less is obtained. Thus,
preferred strength and suitable solubility characteristics for the toner
can be given.

[0150] In addition, with regard to a polymerization reaction temperature,
the polymerization reaction is preferably performed at a temperature
higher than the 10-hour halflife temperature of the polymerization
initiator by 15° C. or more and 35° C. or less. When the
polymerization reaction is performed at a temperature higher than the
10-hour halflife temperature by 15° C. or more and 35° C.
or less, the polymerization reaction is promoted, and hence excessive
branching or crosslinking of the binder resin is easily suppressed.

[0151] Specific examples of the polymerization initiator include:
azo-based or diazo-based polymerization initiators such as
2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile,
1,1'-azobis(cyclohexane-1-carbonitrile),
2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and
azobisisobutyronitrile; and peroxide-based polymerization initiators such
as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl
peroxydicarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide,
lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl
peroxypivalate, di(2-ethylhexyl)peroxydicarbonate, and
di(sec-butyl)peroxydicarbonate. Of those,
di(2-ethylhexyl)peroxydicarbonate and di(sec-butyl)peroxydicarbonate
which are of a peroxydicarbonate type are preferably used because, as
described above, a binder resin which has a low molecular weight and is
also of a linear type molecular structure is easily manufactured.

[0152] When the toner of the present invention is produced by a
polymerization method, a crosslinking agent may be added. The amount of
the agent to be added is preferably 0.001 part by mass or more and 15
parts by mass or less with respect to 100 parts by mass of the
polymerizable monomer.

[0153] Here, as the crosslinking agent, a compound having two or more
polymerizable double bonds is mainly used. Examples thereof include:
aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene;
carboxylates each having two double bonds, such as ethylene glycol
diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol
dimethacrylate; divinyl compounds such as divinylaniline, divinyl ether,
divinyl sulfide, and divinyl sulfone; and a compound having three or more
vinyl groups. Those can be used alone or in admixture of two or more
kinds thereof.

[0154] In the method of producing the toner of the present invention by a
polymerization method, in general, the above-mentioned toner composition
and the like are appropriately added and uniformly dissolved or dispersed
by means of a dispersion machine such as a homogenizer, a ball mill, or
an ultrasonic dispersing device to prepare a polymerizable monomer
composition, and this is suspended into an aqueous medium containing a
dispersion stabilizer. In this case, it is recommended that a high-speed
dispersing device such as a high-speed agitator or the ultrasonic
dispersing device be used to provide a desired toner particle size at a
stroke because the size distribution of the resultant toner particles
becomes sharp. A polymerization initiator may be added simultaneously
with the addition of other additives to the polymerizable monomer, or may
be mixed immediately before suspension into the aqueous medium. In
addition, immediately after granulation, a polymerization initiator
dissolved into the polymerizable monomer or the solvent can be added
before the initiation of a polymerization reaction.

[0155] After granulation, stirring is only required to be performed by an
ordinary agitator to the extent that a particle state is maintained and
the floating and sedimentation of a particle are prevented.

[0156] When the toner of the present invention is produced, a known
surfactant, or a known organic dispersant or inorganic dispersant can be
used as a dispersion stabilizer. Of those, an inorganic dispersant can be
preferably used because the stability of the inorganic dispersant hardly
collapses even when the reaction temperature is changed because the
dispersant has a dispersion stability owing to its steric hindrance
property. In addition, the inorganic dispersant can be easily washed, and
has little adverse effect on the toner. Examples of such inorganic
dispersant include: polyvalent metal phosphates such as tricalcium
phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, and
hydroxyapatite; carbonates such as calcium carbonate and magnesium
carbonate; inorganic salts such as calcium metasilicate, calcium sulfate,
and barium sulfate; and inorganic compounds such as calcium hydroxide,
magnesium hydroxide, and aluminum hydroxide.

[0157] Such inorganic dispersant is preferably used in an amount of 0.2
part by mass or more and 20 parts by mass or less with respect to 100
parts by mass of the polymerizable monomer. In addition, one kind of the
above-mentioned dispersion stabilizers may be used alone, or multiple
kinds thereof may be used in combination. Further, a surfactant may be
used in combination in an amount of 0.001 part by mass or more and 0.1
part by mass or less.

[0158] When each of the inorganic dispersants is used, the inorganic
dispersant may be used as it is. Alternatively, particles of the
inorganic dispersants can be produced in the aqueous medium for obtaining
fine particles. For example, in the case of using tricalcium phosphate,
an aqueous solution of sodium phosphate and an aqueous solution of
calcium chloride are mixed under high-speed stirring, and thus
water-insoluble calcium phosphate can be produced. As a result,
dispersion can be performed with improved uniformity and improved
fineness. At this time, a water-soluble sodium chloride salt is
simultaneously produced as a by-product. The presence of a water-soluble
salt in the aqueous medium is more convenient because the water-soluble
salt suppresses the dissolution of the polymerizable monomer into water
so that ultra-fine toner due to emulsion polymerization is hardly
produced.

[0160] In the step of polymerizing the above-mentioned polymerizable
monomer, the polymerization temperature is set to 40° C. or more,
generally 50° C. or more and 90° C. or less. When the
polymerization is performed at a temperature within the range, a low
melting point substance to be enclosed inside deposits owing to phase
separation, thereby contributing to complete inclusion.

[0161] After that, there is a cooling step of cooling the resultant from a
reaction temperature of 50° C. or more and 90° C. or less
to terminate the polymerization reaction step. At that time, it is
preferred that the cooling be gradually performed so that a state in
which the release agent (a) and the binder resin are compatibilized with
each other be maintained.

[0162] After the termination of the polymerization of the above-mentioned
polymerizable monomer, the resultant polymer particles are filtrated,
washed, and dried by known methods. Thus, toner particles are obtained.
The toner particles are mixed with such an inorganic fine powder as
described later as required so that the inorganic fine powder be caused
to adhere to the surface of each of the toner particles. Thus, the toner
of the present invention can be obtained. In addition, a coarse powder
and a fine powder in the toner particles can be cut by incorporating a
classifying step in the production steps (before the mixing of the
inorganic fine powder).

[0163] The toner in the present invention may have an inorganic fine
powder as well as the toner particles. The inorganic fine powder has a
number-average primary particle diameter of preferably 4 nm or more and
80 nm or less, more preferably 6 nm or more and 40 nm or less. The
inorganic fine powder is added for improving the flowability of the toner
and uniformizing the charging of the toner particles. Further, functions
such as the adjustment of the charge quantity of the toner and an
improvement in its environmental stability can be imparted by subjecting
the inorganic fine powder to a hydrophobic treatment.

[0164] In the present invention, a known measurement method can be
employed as a method of measuring the number-average primary particle
diameter of the inorganic fine powder. Specifically, the measurement can
be performed with a photograph of the toner photographed with a scanning
electron microscope at a certain magnification.

[0165] Silica, titanium oxide, alumina, or the like can be used as the
inorganic fine powder to be used in the present invention. For example,
both dry silica, which is so called dry process silica or fumed silica,
produced by the vapor phase oxidation of a silicon halide and the
so-called wet silica produced from water glass and the like can each be
used as a silica fine powder. However, the dry silica is preferred
because the number of silanol groups present on its surface and in the
silica fine powder is small, and the amount of a production residue such
as Na2O or SO32- is small. A composite fine powder of the
silica and any other metal oxide can also be obtained by using any other
metal halide such as aluminum chloride or titanium chloride together with
the silicon halide in the production step, and such composite fine powder
is also included in the category of the dry silica.

[0166] The addition amount of the inorganic fine powder having a
number-average primary particle diameter of 4 nm or more and 80 nm or
less is preferably 0.1 part by mass or more and 3.0 parts by mass or less
with respect to 100 parts by mass of the toner particles. The content of
the inorganic fine powder can be determined with a calibration curve
created from a standard sample by employing fluorescent X-ray analysis.

[0167] In the present invention, the inorganic fine powder is preferably
subjected to a hydrophobic treatment because the environmental stability
of the toner can be improved. One kind of treatment agents such as a
silicone varnish, various modified silicone varnishes, a silicone oil,
various modified silicone oils, a silane compound, a silane coupling
agent, and other organosilicon compounds and organic titanium compounds
may be used alone as a treatment agent to be used in the hydrophobic
treatment of the inorganic fine powder, or two or more kinds thereof may
be used in combination.

[0168] The inorganic fine powder is preferably treated with the silicone
oil out of the above-mentioned treatment agents, and is more preferably
treated with the silicone oil simultaneously with the hydrophobic
treatment of the inorganic fine powder with the silane compound or after
the treatment. Such treatment method for the inorganic fine powder is,
for example, as described below. A silylation reaction is performed with
the silane compound as a first-stage reaction so that a silanol group be
caused to disappear by a chemical bond. After that, the formation of a
hydrophobic thin film on the surface of the inorganic fine powder with
the silicone oil can be performed as a second-stage reaction.

[0169] The above-mentioned silicone oil has a viscosity at 25° C.
of preferably 10 mm2/s or more and 200,000 mm2/s or less, more
preferably 3,000 mm2/s or more and 80,000 mm2/s or less.

[0171] As a method of treating the inorganic fine powder with the silicone
oil, there is given, for example, a method involving directly mixing the
inorganic fine powder being treated with a silane compound and the
silicone oil by means of a mixer such as a Henschel mixer, or a method
involving spraying the silicone oil on the inorganic fine powder.
Alternatively, a method involving dissolving or dispersing the silicone
oil in a suitable solvent, then adding the inorganic fine powder, mixing
the whole, and removing the solvent may be used. In view of the advantage
that the inorganic fine powder agglomerates in a relatively small amount,
a method involving spraying the silicone oil is more preferred.

[0172] The treatment amount of the silicone oil is preferably 1 part by
mass or more and 40 parts by mass or less, more preferably 3 parts by
mass or more and 35 parts by mass or less with respect to 100 parts by
mass of the inorganic fine powder.

[0173] The inorganic fine powder to be used in the present invention has a
specific surface area measured by a BET method based on nitrogen
adsorption of preferably 20 m2/g or more and 350 m2/g or less,
more preferably 25 m2/g or more and 300 m2/g or less for
imparting good flowability to the toner. The specific surface area is
calculated by employing a BET multipoint method with a specific surface
area-measuring apparatus AUTOSORB 1 (manufactured by Yuasa Ionics Inc.)
while causing a nitrogen gas to adsorb to the sample surface according to
the BET method.

[0174] Further, in the toner of the present invention, a small amount of
any other additive may also be used, for example, a lubricant powder such
as a fluororesin powder, a zinc stearate powder, or a polyvinylidene
fluoride powder; an abrasive such as a cerium oxide powder, a silicon
carbide powder, or a strontium titanate powder; a flowability-imparting
agent such as a titanium oxide powder or an aluminum oxide powder; a
caking inhibitor; or organic and/or inorganic fine particles opposite in
polarity as a developing performance-improving agent. The surface of any
such additive can be subjected to a hydrophobic treatment before the
additive is used.

[0175] An example of an image-forming apparatus in which the toner of the
present invention can be suitably used is specifically described with
reference to drawings.

[0176] In an image-forming apparatus of FIG. 1, the periphery of a
photosensitive member 100 is provided with a primary charging roller 117,
a developing unit 140, a transfer charging roller 114, a cleaner 116, a
register roller 124, and the like. In addition, the photosensitive member
100 is charged to, for example, -700 V by the primary charging roller 117
(applied voltages are an AC voltage of -2.0 kVpp and a DC voltage of -700
Vdc). In addition, laser light 123 is applied from a laser-generating
apparatus 121 to the photosensitive member 100 so that the photosensitive
member be exposed. An electrostatic latent image on the photosensitive
member 100 is developed with a one-component magnetic developer by the
developing unit 140, and is then transferred onto a transfer material by
the transfer charging roller 114 brought into abutment with the
photosensitive member through the transfer material. The transfer
material carrying the toner image is conveyed to a fixing unit 126 by a
conveying belt 125 so that the toner image be fixed on the transfer
material. In addition, the toner remaining in part on the photosensitive
member is cleaned by the cleaner 116.

[0177] As illustrated in FIG. 2, the developing unit 140 is provided with
a cylindrical toner carrier 102 (which may hereinafter be referred to as
"developing sleeve") made of a non-magnetic metal such as aluminum or
stainless steel, the developing sleeve being brought close to the
photosensitive member 100, and the gap between the photosensitive member
100 and the developing sleeve 102 is maintained at about 300 μm by,
for example, a developing sleeve/photosensitive member gap-holding member
(not shown). A magnet roller 104 is fixed and provided in the developing
sleeve 102 so as to be concentric with the developing sleeve, provided
that the developing sleeve 102 is rotatable.

[0178] As illustrated in the figure, the magnet roller 104 is provided
with multiple magnetic poles, and the magnetic poles S1, N1, S2, and N2
affect the development, the regulation of a toner coat amount, the
take-up and conveyance of the toner, and the prevention of the blowout of
the toner, respectively. The toner is applied to the developing sleeve
102 by a toner-applying roller 141, and is then conveyed while adhering
to the developing sleeve. A developing blade 103 as a member for
regulating the amount of the toner to be conveyed is provided, and the
amount of the toner to be conveyed to a developing region is controlled
by the abutment pressure of the developing blade 103 against the
developing sleeve 102. In the developing region, DC and AC developing
biases are applied between the photosensitive member 100 and the
developing sleeve 102, and the developer on the developing sleeve flies
onto the photosensitive member 100 depending on the electrostatic latent
image to turn the image into a visible image.

[0179] Next, methods of measuring various physical properties according to
the present invention are described.

[0180] The weight-average particle diameter (D4) of the toner is
calculated in the following manner. As a measuring apparatus, a precision
grain size distribution measuring apparatus based on a pore electrical
resistance method provided with a 100-μm aperture tube "Coulter
Counter Multisizer 3" (registered trademark, manufactured by Beckman
Coulter, Inc.) is used. For setting measurement conditions and analyzing
measurement data, the dedicated software attached to the apparatus
"Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman
Coulter, Inc) is used. It should be noted that the measurement is
performed with the number of effective measurement channels set to
25,000.

[0181] An electrolyte solution prepared by dissolving reagent grade sodium
chloride in ion-exchanged water to have a concentration of about 1 mass
%, for example, an "ISOTON II" (manufactured by Beckman Coulter, Inc) can
be used in the measurement.

[0182] It should be noted that setting for the dedicated software was made
as described below prior to the measurement and the analysis.

[0183] In the "change standard measurement method (SOM)" screen of the
dedicated software, the total count number of a control mode is set to
50,000 particles, the number of times of measurement is set to 1, and a
value obtained by using "standard particle having a particle diameter of
10.0 μm" (manufactured by Beckman Coulter, Inc) is set as a Kd value.
A threshold and a noise level are automatically set by pressing a
"threshold/noise level measurement button." In addition, the current is
set to 1,600 μA, the gain is set to 2, the electrolyte solution is set
to an ISOTON II, and a check mark is placed in a check box as to whether
"the aperture tube is flushed after the measurement."

[0184] In the "setting for conversion from pulse to particle diameter"
screen of the dedicated software, the bin interval is set to a
logarithmic particle diameter, the number of particle diameter bins is
set to 256, and the particle diameter range is set to the range of 2
μm to 60 μm.

[0185] A specific measurement method is as described below.

(1) About 200 ml of the electrolyte solution are put into a 250-ml
round-bottom beaker made of glass dedicated for the Multisizer 3. The
beaker is set in a sample stand, and the electrolyte solution in the
beaker is stirred with a stirrer rod at 24 rotations/sec in a
counterclockwise direction. Then, dirt and bubbles in the aperture tube
are removed by the "aperture flush" function of the dedicated software.
(2) About 30 ml of the electrolyte solution are put into a 100-ml
flat-bottom beaker made of glass. About 0.3 ml of a diluted solution
prepared by diluting a "Contaminon N" (a 10-mass % aqueous solution of a
neutral detergent for washing a precision measuring device formed of a
nonionic surfactant, an anionic surfactant, and an organic builder and
having a pH of 7, manufactured by Wako Pure Chemical Industries, Ltd.)
with ion-exchanged water by about three mass fold is added as a
dispersant to the electrolyte solution. (3) An ultrasonic dispersing unit
"Ultrasonic Dispersion System Tetra 150" (manufactured by Nikkaki Bios
Co., Ltd.) in which two oscillators each having an oscillatory frequency
of 50 kHz are provided so as to be mutually out of phase by 180°
and which has an electrical output of 120 W is prepared. About 3.3 l of
ion-exchanged water is put into the water tank of the ultrasonic
dispersing unit. About 2 ml of the Contaminon N are put into the water
tank. (4) The beaker in the item (2) is set in the beaker fixing hole of
the ultrasonic dispersing unit, and the ultrasonic dispersing unit is
operated. Then, the height position of the beaker is adjusted in order
that the resonation of the liquid level of the electrolyte solution in
the beaker be maximum. (5) About 10 mg of the toner is gradually added to
and dispersed in the electrolyte solution in the beaker in the item (4)
in a state in which the electrolyte solution is irradiated with the
ultrasonic wave. Then, the ultrasonic dispersion treatment is continued
for additional 60 seconds. It should be noted that the temperature of
water in the water tank is appropriately adjusted so as to be 10°
C. or more and 40° C. or less upon ultrasonic dispersion. (6) The
electrolyte solution in the item (5) in which the toner has been
dispersed is dropped with a pipette to the round-bottom beaker in the
item (1) placed in the sample stand, and the concentration of the toner
to be measured is adjusted to about 5%. Then, measurement is performed
until the particle diameters of 50,000 particles are measured. (7) The
measurement data is analyzed with the dedicated software attached to the
apparatus, and the weight-average particle diameter (D4) is calculated.
It should be noted that "average diameter" on the "analysis/volume
statistics (arithmetic average)" screen of the dedicated software when
the dedicated software is set to graph/volume % is the weight-average
particle diameter (D4).

<Measurement of Average Circularity of Toner>

[0186] The average circularity of toner is measured at the time of
correction operation and under analysis conditions with a flow-type
particle image analyzer "FPIA-3000" (manufactured by SYSMEX CORPORATION).

[0187] A specific measurement method is as described below. First, about
20 ml of ion-exchanged water from which impure solid and the like have
been removed in advance are put into a container made of glass. About 0.2
ml of a diluted solution prepared by diluting "Contaminon N" (a 10-mass %
aqueous solution of a neutral detergent for washing a precision measuring
unit formed of a nonionic surfactant, an anionic surfactant, and an
organic builder and having a pH of 7, manufactured by Wako Pure Chemical
Industries, Ltd.) with ion-exchanged water by about three mass fold is
added as a dispersant to the container. Further, about 0.02 g of a
measurement sample is added to the container, and then the mixture is
subjected to a dispersion treatment with an ultrasonic dispersing unit
for 2 minutes so that a dispersion liquid for measurement be obtained. At
that time, the dispersion liquid is appropriately cooled so as to have a
temperature of 10° C. or more and 40° C. or less. A desktop
ultrasonic cleaning and dispersing unit having an oscillatory frequency
of 50 kHz and an electrical output of 150 W (such as a "VS-150"
(manufactured by VELVO-CLEAR)) is used as the ultrasonic dispersing unit.
A predetermined amount of ion-exchanged water is put into a water tank,
and about 2 ml of the Contaminon N are added to the water tank.

[0188] The flow-type particle image analyzer mounted with an "UPlanApro"
(magnification: 10, numerical aperture: 0.40) as an objective lens was
used in the measurement, and a particle sheath "PSE-900A" (manufactured
by SYSMEX CORPORATION) was used as a sheath liquid. The dispersion liquid
prepared in accordance with the procedure is introduced into the
flow-type particle image analyzer, and 3,000 toner particles are
subjected to measurement according to the total count mode of an HPF
measurement mode. Then, the average circularity of the toner particles is
determined with a binarization threshold at the time of particle analysis
set to 85% and with particle diameters to be analyzed limited to those
corresponding to a circle-equivalent diameter of 1.985 μm or more and
less than 39.69 μm.

[0189] On the measurement, automatic focusing is performed with standard
latex particles (obtained by diluting, for example, "RESEARCH AND TEST
PARTICLES Latex Microsphere Suspensions 5200A" manufactured by Duke
Scientific with ion-exchanged water) prior to the initiation of the
measurement. After that, focusing is preferably performed every two hours
from the initiation of the measurement.

[0190] It should be noted that in each example of the present application,
a flow-type particle image analyzer which had been subjected to a
calibration operation by SYSMEX CORPORATION and received a calibration
certificate issued by SYSMEX CORPORATION was used. The measurement was
performed under measurement and analysis conditions identical to those at
the time of the reception of the calibration certificate except that
particle diameters to be analyzed were limited to those corresponding to
a circle-equivalent diameter of 1.985 μm or more and less than 39.69
μm.

[0192] 0.03 g of the toner is dispersed in 10 ml of tetrahydrofuran. The
resultant dispersion liquid is shaken with a shaker at 25° C. for
24 hours, and is then filtrated through a 0.2-μm filter. The resultant
filtrate is used as a sample.

[0195] It should be noted that data analysis was performed with an ASTRA
for Windows 4.73.04 (Wyatt Technology Corp.).

<SEC-MALLS Measurement of Toner at 135° C. (Mn (135°
C.))>

[0196] The number-average molecular weight Mn (135° C.) of the
o-dichlorobenzene-soluble components of the toner of the present
invention at 135° C. were determined by SEC-MALLS measurement.

[0197] 0.03 g of the toner is dispersed in 10 ml of o-dichlorobenzene. The
resultant dispersion liquid is shaken with a shaker at 135° C. for
24 hours, and is then filtrated through a 0.2-μm filter. The resultant
filtrate is used as a sample.

[0199] It should be noted that data analysis was performed with an ASTRA
for Windows 4.73.04 (Wyatt Technology Corp.).

<Measurement of Proportion of Components Having Molecular Weight of 500
or Less in Tetrahydrofuran-Soluble Components of Toner, and
Weight-Average Molecular Weight Mw and Number-Average Molecular Weight Mn
of Polyester Resin>

[0200] A proportion of components having a molecular weight of 500 or less
in the tetrahydrofuran-soluble components of the toner, and the weight-
and number-average molecular weights of the polyester resin are measured
by gel permeation chromatography (GPC) as described below.

[0201] First, the toner or the polyester resin is dissolved in
tetrahydrofuran (which may hereinafter be referred to as "THF") at room
temperature over 24 hours. Then, the resultant solution is filtrated
through a solvent-resistant membrane filter "Maeshori Disk" (manufactured
by TOSOH CORPORATION) having a pore diameter of 0.2 μm so that a
sample solution be obtained. It should be noted that the sample solution
is prepared so that the concentration of components soluble in THF be
about 0.8 mass %. The measurement is performed with the sample solution
under the following conditions.

[0202] The proportion of components having a molecular weight of 500 or
less in the tetrahydrofuran-soluble components of the toner is the
proportion of the area in a chart obtained by this GPC measurement
(abscissa: retention time, ordinate: voltage detected by RI). In the
calculation of the molecular weight of the sample, a molecular weight
calibration curve prepared with standard polystyrene resins (for example,
product names "TSK standard polystyrenes F-850, F-450, F-288, F-128,
F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, and A-500"
manufactured by Tosoh Corporation) is used. The weight-average molecular
weight Mw and number-average molecular weight Mn of the polyester resin
were calculated from the molecular weight distribution obtained by
applying the molecular weight calibration curve to the chart obtained by
the GPC measurement.

[0203] <Measurement of Peak Top Temperature of Maximum Endothermic Peak
of Release Agent>

[0204] The peak top temperature (melting point) of the maximum endothermic
peak of a release agent is measured with a differential scanning
calorimeter "Q1000" (manufactured by TA Instruments) in conformity with
ASTM D3418-82.

[0205] The melting points of indium and zinc are used for the temperature
correction of the detecting portion of the apparatus, and the heat of
fusion of indium is used for the correction of heat quantity.

[0206] Specifically, about 10 mg of the release agent are precisely
weighed. The release agent is put into an aluminum pan, and then the
measurement is performed with an empty aluminum pan as a reference in the
measuring temperature range of 30° C. to 200° C. at a
heating rate of 10° C./min. It should be noted that in the
measurement, the temperature is increased to 200° C. once,
subsequently decreased to 30° C., and then increased again. The
maximum endothermic peak of a DSC curve in the temperature range of
30° C. to 200° C. in the second temperature increase
process is defined as the endothermic peak top of the endothermic curve
in the DSC of the release agent.

<Method of Measuring Acid Value of Release Agent>

[0207] The acid value of the release agent is measured in conformity with
JIS K 1557-1970. A specific measurement method is as described below.

[0208] First, 2 g of the release agent are precisely weighed (W (g)). The
sample is put into a 200-ml three-necked flask, and 100 ml of a mixed
solution of toluene and ethanol (2:1) are added to dissolve the sample
over 5 hours. Then, a phenolphthalein solution is added as an indicator.
Using a 0.1 N KOH/alcohol solution, the above-mentioned solution is
titrated by means of a buret. The amount of the KOH solution at this time
is represented by S (ml). Blank test is performed, and the amount of the
KOH solution at this time is represented by B (ml)

[0209] The acid value is calculated from the following equation.

Acid value=[(S-B)×f×5.61]/W

(f: factor of KOH solution)

[0210] <Solubility of Release Agent in Binder Resin>

[0211] The solubility of a release agent in the binder resin is measured
as described below.

[0214] The above-mentioned materials are mixed in an agate mortar so that
a sample 1 be obtained.

[0215] A differential scanning calorimeter "Q1000" (manufactured by TA
Instruments) or "DSC2920" (manufactured by TA Instruments) can be used as
a measuring apparatus, and the measurement is performed in conformity
with ASTM D3418-82.

[0216] About 10 mg of the sample 1 is precisely weighed and put into an
aluminum pan, and then the endotherm of the sample is measured with, for
example, "Q1000" and with an empty aluminum pan as a reference according
to the following sequence. The melting points of indium and zinc are used
for the temperature correction of the detecting portion of the apparatus,
and the heat of fusion of indium is used for the correction of the heat
quantity.

[0217] Then, the solubility is determined from the following equation
where ΔH1 represents the endothermic peak heat quantity of a second
cycle and ΔH2 represents the endothermic peak heat quantity of a
fourth cycle. It should be noted that each endothermic peak heat quantity
is the heat quantity of the maximum endothermic peak in a DSC curve in
the temperature range of 30 to 120° C. during heating.

Solubility=(1-ΔH2/ΔH1)×100

<Sequence>

First Cycle:

[0218] Keep the temperature at 30° C. for 1 minute.

[0219] Increase the temperature to 60° C. at a rate of 2°
C./min.

[0220] Keep the temperature for 10 minutes after temperature increase.

[0221] Decrease the temperature to 30° C. at a rate of 10°
C./min.

Second Cycle:

[0222] Keep the temperature at 30° C. for 1 minute.

[0223] Increase the temperature to 120° C. at a rate of 10°
C./min.

[0224] Keep the temperature for 10 minutes after temperature increase.

[0225] Decrease the temperature to 30° C. at a rate of 10°
C./min.

Third Cycle:

[0226] Keep the temperature at 30° C. for 1 minute.

[0227] Increase the temperature to 60° C. at a rate of 2°
C./min.

[0228] Keep the temperature for 10 minutes after temperature increase.

[0229] Decrease the temperature to 30° C. at a rate of 10°
C./min.

Fourth Cycle:

[0230] Keep the temperature at 30° C. for 1 minute.

[0231] Increase the temperature to 120° C. at a rate of 10°
C./min.

[0232] Keep the temperature for 10 minutes after temperature increase.

[0233] Decrease the temperature to 30° C. at a rate of 10°
C./min.

[0234] Although the above-mentioned styrene-acrylic resin is preferably
used, when its preparation is difficult, the measurement may be performed
with a styrene-acrylic resin having a glass transition temperature of
54.0° C.±1.0° C., a number-average molecular weight (Mn)
of 20,000±2,000, and a weight-average molecular weight (Mw) of
200,000±20,000. As long as the parameters fall within the
above-mentioned ranges, substantially the same value for the solubility
is obtained.

[0235] In addition, a binder resin having a low molecular weight or a
binder resin with its branched structure adjusted has been used as the
binder resin in the present invention. It has been confirmed that in this
case, the absolute values of the solubilities change but which one of the
release agents has a larger solubility in the binder resin than that of
the other does not change. Accordingly, in the present invention, the
above-mentioned measured values were used as the solubilities of the
release agent (a) and the release agent (b) in the binder resin.

<Total Energy of Toner Particles>

[0236] The total energy of the toner particles in the present invention
when a propeller type blade is caused to penetrate a toner particle layer
at an agitation rate of 100 mm/sec is measured with a powder flowability
analyzer Powder Rheometer FT-4 (manufactured by Freeman Technology)
(which may hereinafter be referred to as "FT-4").

[0237] Specifically, the measurement is performed by the following
operations. It should be noted that a blade dedicated for measurement
with the FT-4 having a diameter of 48 mm (which may hereinafter be
abbreviated as "blade." See, FIGS. 3A and 3B: the blade has its rotation
axis at the center of its blade plate measuring 48 mm by 10 mm in the
direction normal to the center, material: SUS, model: C210, twisted
smoothly in a counterclockwise direction such that both outermost edge
portions (portions each placed at a distance of 24 mm from the rotation
axis) each form an angle of 70°, and portions each placed at a
distance of 12 mm from the rotation axis each form an angle of
35°) is used as a propeller type blade in each of all the
operations.

[0238] 100 g of magnetic toner particles left to stand under an
environment having a temperature of 23° C. and a humidity of 60%
for 3 days or longer are put into a cylindrical split cell dedicated for
measurement with the FT-4 having a diameter of 50 mm and a volume of 160
ml (which may hereinafter be abbreviated as "cell." model: C203, height
from the bottom surface of the container to a split portion: 82 mm,
material: glass) so that a powder layer (toner particle layer) is formed.

(1) Conditioning Operation

[0239] (a) The blade is caused to penetrate from the surface of the powder
layer to a position at a distance of 10 mm from the bottom surface of the
powder layer under the following conditions: the rotational speed of the
blade in a clockwise direction relative to the surface of the powder
layer (direction in which the powder layer is loosened by the rotation of
the blade) is set so that the circumferential speed of each outermost
edge portion be 60 (mm/sec); and the speed at which the blade is caused
to penetrate into the powder layer in the direction perpendicular to the
layer is set so that the angle formed between a path taken by each
outermost edge portion of the blade during the movement and the surface
of the powder layer be 5 (deg) (which may hereinafter be abbreviated as
"angle formed"). After that, the operation of causing the blade to
penetrate into a position at a distance of 1 mm from the bottom surface
of the magnetic powder layer is performed under the following conditions:
the rotational speed of the blade in the clockwise direction relative to
the surface of the powder layer is 60 (mm/sec); and the speed at which
the blade is caused to penetrate into the powder layer in the direction
perpendicular to the layer is such that the angle formed is 2 (deg).
After that, the blade is moved to a position at a distance of 100 mm from
the bottom surface of the powder layer under the following conditions so
as to be pulled out the rotational speed of the blade in the clockwise
direction relative to the surface of the powder layer is 60 (mm/sec); and
the speed at which the blade is pulled out from the powder layer is such
that the angle formed is 5 (deg). After the completion of the pulling
out, the blade is rotated in the clockwise and counterclockwise
directions alternately to a small extent so that the toner adhering to
the blade is shaken off. (b) The series of operations in the
above-mentioned item (1)-(a) is performed five times so that air involved
in the toner powder layer is removed. Thus, a stable magnetic toner
powder layer is produced.

(2) Split Operation

[0240] The powder layer is leveled off with the split portion of the
above-mentioned cell dedicated for measurement with the FT-4, and the
toner in the upper portion of the powder layer is removed, thereby
forming powder layers having the same volume.

(3) Measurement Operation

[0241] (a) A conditioning operation similar to that of the above-mentioned
item (1)-(a) is performed once. Next, the blade is caused to penetrate
into a position at a distance of 10 mm from the bottom surface of a
powder layer under the following conditions: the rotational speed of the
blade in a counterclockwise direction relative to the surface of the
powder layer (direction in which the powder layer is squeezed by the
rotation of the blade) is set to 100 (mm/sec); and the speed at which the
blade is caused to penetrate into the powder layer in the direction
perpendicular to the layer is such that the angle formed is 5 (deg).
After that, the operation of causing the blade to penetrate into a
position at a distance of 1 mm from the bottom surface of the powder
layer is performed under the following conditions: the rotational speed
of the blade in the clockwise direction relative to the surface of the
powder layer is set to 60 (mm/sec); and the speed at which the blade is
caused to penetrate into the powder layer in the direction perpendicular
to the layer is such that the angle formed is 2 (deg). After that, the
blade is pulled out to a position at a distance of 100 mm from the bottom
surface of the powder layer under the following conditions: the
rotational speed of the blade in the clockwise direction relative to the
surface of the powder layer is set to 60 (mm/sec); and the speed at which
the blade is pulled out from the powder layer in the direction
perpendicular to the layer is such that the angle formed is 5 (deg).
After the completion of the pulling out, the blade is rotated in the
clockwise and counterclockwise directions alternately to a small extent
so that the toner adhering to the blade is shaken off. (b) The
above-mentioned series of operations is repeated seven times. At the
seventh repetition, measurement is initiated from the position at a
distance of 100 mm from the bottom surface of the toner powder layer at a
rotational speed of the blade of 100 (mm/sec). A sum total of a rotation
torque and a vertical load obtained at the time when the blade is caused
to penetrate to the position at a distance of 10 mm from the bottom
surface is defined as a total energy when an agitation rate is 100
mm/sec.

<Polymerization Conversion Degree>

[0242] A polymerization conversion degree in the suspension polymerization
method was calculated by determining the amount of a residual styrene
monomer. That is, the polymerization conversion degree when the whole
amount of an added styrene monomer was detected in the following
measurement was set to 0%, and the polymerization conversion degree when
the styrene monomer was no longer detected in the toner as a
polymerization reaction progressed was set to 100%.

[0243] The amount of the styrene monomer remaining in the toner is
measured by gas chromatography (GC) as described below.

[0244] About 500 mg of the toner is precisely weighed and put into a
sample bottle. About 10 g of acetone that have been precisely weighed is
added to the toner, and then the sample bottle is capped. After that, the
contents are mixed well, and then the mixture is irradiated with an
ultrasonic wave from a desktop ultrasonic cleaning unit having an
oscillatory frequency of 42 kHz and an electrical output of 125 W (such
as a product available under the trade name "B2510J-MTH" from Branson
Co.) for 30 minutes. After that, the resultant is filtrated through a
solvent-resistant membrane filter "Maishori Disk" (manufactured by TOSOH
CORPORATION) having a pore diameter of 0.2 μm, and then 2 μl of the
filtrate are analyzed by gas chromatography. Then, the remaining amount
of the residual styrene monomer is calculated from a calibration curve
created in advance with styrene.

[0245] About 1.5 g of the toner is weighed (W1 g) and placed in extraction
thimble filter (such as a product available under the trade name "No.
86R" (size: 28×100 mm) from Advantec Toyo Co.) which has been
weighed in advance. The resultant is set in a Soxhlet extractor, and is
then subjected to extraction with 200 ml of tetrahydrofuran as a solvent
for 10 hours. At this time, the extraction is performed at such a reflux
rate that the cycle of the extraction with the solvent is once per about
five minutes.

[0246] After the termination of the extraction, the extraction thimble is
taken out and air-dried. After that, the extraction thimble filter is
dried in a vacuum at 40° C. for 8 hours, and then the mass of the
extraction thimble filter including the extraction residue is weighed.
The mass (W2 g) of the extraction residue is calculated by subtracting
the mass of the extraction thimble filter from the weighted mass.

[0247] Next, the content (W3 g) of the other components than the resin
component is determined by the following procedure. About 2 g of the
toner is weighed (Wa g) in a 30-ml magnetic crucible that has been
weighed in advance. The crucible is placed in an electric furnace, heated
at about 900° C. for about 3 hours, left standing to cool in the
electric furnace, and left standing to cool under normal temperature in a
desiccator for 1 hour or more. Then, the mass of the crucible containing
the incineration residual ash is weighed, and the mass of the
incineration residual ash (Wb g) is calculated by subtracting the mass of
the crucible from the weighed mass. Then, the mass (W3 g) of the
incineration residual ash in W1 g of the sample is calculated from the
following equation.

W3=W1×(Wb/Wa)

[0248] In this case, the content of the tetrahydrofuran-insoluble
component is determined from the following equation.

[0249] Content of tetrahydrofuran-insoluble component

(mass %)={(W2-W3)/(W1-W3)}×100

[0250] Hereinafter, the present invention is described in more detail by
way of examples and comparative examples. It should be noted that the
term "part(s)" refers to "part(s) by mass" unless otherwise stated.

<Monofunctional or Bifunctional Ester Wax>

[0251] Waxes shown in Table 1 below were each prepared as a monofunctional
or bifunctional ester wax.

[0254] The following components were put into a reaction tank provided
with a cooling tube, an agitator, and a nitrogen-introducing tube, and
were then subjected to a reaction at 230° C. in a stream of
nitrogen for 10 hours while produced water was removed by distillation.

[0255] Next, the components were subjected to a reaction under a reduced
pressure of 5 to 20 mmHg, and then the resultant was cooled to
180° C. when its acid value became 2 mgKOH/g or less. 62 Parts of
trimellitic anhydride was added to the resultant, and then the mixture
was subjected to a reaction under normal pressure in a hermetically
sealed state for 2 hours. After that, the resultant was taken out and
cooled to room temperature, followed by pulverization. Thus, a polyester
resin was obtained. The resultant polyester resin 1 had a weight-average
molecular weight Mw of 10,500, a number-average molecular weight Mn of
3,800, and an acid value of 6.

<Synthesis of Polyester Resin 2>

[0256] The following components were put into a reaction tank provided
with a cooling tube, an agitator, and a nitrogen-introducing tube, and
were then subjected to a reaction at 230° C. in a stream of
nitrogen for 10 hours while produced water was removed by distillation.

[0257] Next, the components were subjected to a reaction under a reduced
pressure of 5 to 20 mmHg, and then the resultant was cooled to
180° C. when its acid value became 2 mgKOH/g or less. 62 Parts of
trimellitic anhydride was added to the resultant, and then the mixture
was subjected to a reaction under normal pressure in a hermetically
sealed state for 2 hours. After that, the resultant was taken out and
cooled to room temperature, followed by pulverization. Thus, a polyester
resin was obtained. The resultant polyester resin 2 had a weight-average
molecular weight Mw of 10,300, a number-average molecular weight Mn of
4,000, and an acid value of 7.

[0259] The above-mentioned raw materials were dropped to 200 parts of
heated xylene over 4 hours. Further, polymerization was completed under
xylene reflux. A styrene-acrylic resin 1 thus obtained had a
weight-average molecular weight Mw measured by SEC-MALLS of 100,000, an
Rw/Mw of 5.0×10-4, and a glass transition temperature Tg of
60° C.

<Production Example of Magnetic Iron Oxide 1>

[0260] In an aqueous ferrous sulfate solution, a sodium hydroxide solution
(containing 1 mass % of sodium hexametaphosphate in terms of P with
respect to Fe) was mixed in an amount of 1.0 equivalent with respect to
the iron ions, to prepare an aqueous solution containing ferrous
hydroxide. Air was blown into the aqueous solution while the pH of the
aqueous solution was kept at 9, and an oxidation reaction was performed
at 80° C., thereby preparing a slurry liquid for producing a seed
crystal.

[0261] Next, to this slurry liquid, an aqueous ferrous sulfate solution
was added so as to be in an amount of 1.0 equivalent with respect to the
initial alkali content (the sodium component in the sodium hydroxide).
Then, the pH of the slurry liquid was kept at 8, and an oxidation
reaction was advanced while air was blown into the liquid. The pH of the
liquid was adjusted to about 6 at the terminal stage of the oxidation
reaction. 1.5 parts of n-C6H13Si(OCH3)3 was added as
a silane coupling agent with respect to 100 parts of a magnetic iron
oxide, and then the mixture was sufficiently agitated. Hydrophobic iron
oxide particles thus produced were washed, filtrated, and dried by
ordinary methods. After agglomerating particles had been subjected to a
pulverizing treatment, a heat treatment was performed at a temperature of
70° C. for 5 hours. Thus, a magnetic iron oxide 1 was obtained.

[0262] The magnetic iron oxide 1 had an average particle diameter of 0.25
μm, and a saturation magnetization and a residual magnetization in a
magnetic field of 79.6 kA/m (1,000 Oe) of 67.3 Am2/kg (emu/g) and
4.0 Am2/kg (emu/g), respectively.

<Production of Toner 1>

[0263] 450 Parts of a 0.1-mol/L aqueous solution of Na3PO4 was
put into 720 parts of ion-exchanged water, and then the mixture was
heated to a temperature of 60° C. After that, 67.7 parts of a
1.0-mol/L aqueous solution of CaCl2 was added to the resultant.
Thus, an aqueous medium containing a dispersion stabilizer was obtained.

[0264] The above-mentioned formulations were uniformly dispersed and mixed
with an attritor (Mitsui Miike Machinery Co., Ltd.). The resultant
monomer composition was heated to a temperature of 60° C., and
then 10 parts of E4 as a release agent (a), 5 parts of P2 as a release
agent (b), and 4 parts of the polymerization initiator R1 (having a
10-hour halflife temperature of 51° C.) were mixed and dissolved
in the composition. Thus, a polymerizable monomer composition was
obtained.

[0265] The above-mentioned polymerizable monomer composition was put into
the aqueous medium, and then the mixture was agitated at a temperature of
60° C. under an N2 atmosphere with a TK-homomixer (Tokushu
Kika Kogyo Co.) at 10,000 rpm for 15 minutes so as to be granulated.

[0266] After that, a polymerization reaction was performed at a reaction
temperature of 70° C. (temperature higher than the 10-hour
halflife temperature of R1 by 19° C.) for 360 minutes by agitating
the resultant with a paddle agitation blade.

[0267] After that, the resultant suspension was cooled to room temperature
at a rate of 3° C. per minute, and then hydrochloric acid was
added to dissolve the dispersant. The resultant was filtrated, washed
with water, and dried. Thus, toner particles 1 were obtained.

[0268] 100 Parts of the toner particles 1 was mixed with 1.0 part of a
hydrophobic silica fine powder that is obtained by treating silica having
a primary particle diameter of 12 nm with hexamethyldisilazane and then
with silicone oil and has a BET specific surface area after the treatment
of 120 m2/g with a Henschel mixer (Mitsui Miike Machinery Co.,
Ltd.). Thus, Toner 1 was prepared. Tables 4 and 5 show conditions for the
production of Toner 1 and its physical properties.

<Production of Toners 2 to 27>

[0269] Toners 2 to 27 were obtained by changing the kinds and amounts of
the polyester resin, the release agent (a), the release agent (b), and
the polymerization initiator, the reaction temperature, and the rate of
temperature decrease of the suspension in the cooling step for
terminating the polymerization reaction in the production of Toner 1 as
shown in Table 4. Tables 4 and 5 show conditions for the production of
Toners 2 to 27 and their physical properties. It should be noted that in
the case of each of Toner 12, Toner 21, Toner 23, and Toner 25, the
polymerization initiator is further added at the time point when the
polymerization conversion degree is 80%.

<Production of Toner 28>

[0270] Polymerizable monomers for a core formed of 80.5 parts of styrene
and 19.5 parts of n-butyl acrylate (calculated Tg of a copolymer to be
obtained=55° C.), 90 parts of the magnetic iron oxide 1, 1 part of
a charge control agent (manufactured by HODOGAYA CHEMICAL CO., LTD.,
trade name: Spilon Black TRH), 0.3 part of divinylbenzene, 0.8 part of
t-dodecyl mercaptan, 10 parts of pentaerythritol tetrastearate (stearic
acid purity: about 60%), and 2 parts of a natural gas-based
Fischer-Tropsch wax (manufactured by D Shell MS Co., trade name: FT-100,
peak top temperature of the maximum endothermic peak: 92° C.) were
agitated and mixed with a homomixer capable of mixing with a high shear
force (TK type, manufactured by Tokushu Kika Kogyo Co.) at a number of
revolutions of 12,000 rpm so as to be uniformly dispersed. Thus, a
polymerizable monomer composition for a core (mixed liquid) was obtained.

[0271] Meanwhile, 5 parts of methyl methacrylate (calculated
Tg=105° C.) and 100 parts of water were subjected to a fine
dispersion treatment with an ultrasonic emulsifier. Thus, an aqueous
dispersion of a polymerizable monomer for a shell was obtained. With
regard to the particle diameter of a droplet of the polymerizable monomer
for a shell, the D90 measured with a Microtrac particle diameter
distribution analyzer by adding the obtained droplet to a 1% aqueous
solution of sodium hexametaphosphate at a concentration of 3% was 1.6
μm. On the other hand, an aqueous solution prepared by dissolving 6.9
parts of sodium hydroxide (alkali metal hydroxide) in 50 parts of
ion-exchanged water was gradually added to an aqueous solution obtained
by dissolving 9.8 parts of magnesium chloride (water-soluble polyvalent
metal salt) in 250 parts of ion-exchanged water under agitation. Thus, a
dispersion liquid of a magnesium hydroxide colloid (colloid of a hardly
water-soluble metal compound) was prepared. The particle diameter
distribution of the above-mentioned colloid thus produced was measured
with a Microtrac particle diameter distribution analyzer (manufactured by
NIKKISO CO., LTD.). As a result, the particle diameter D50 (50%
cumulative value of the number particle diameter distribution) was 0.38
μm and the particle diameter D90 (90% cumulative value of the number
particle diameter distribution) was 0.82 μm. The measurement with the
Microtrac particle diameter distribution analyzer was performed under the
following conditions: a measuring range of 0.12 to 704 μm, a measuring
time of 30 seconds, and ion-exchanged water as a medium.

[0272] The above-mentioned polymerizable monomer composition for a core
was put and mixed into the dispersion liquid of the magnesium hydroxide
colloid obtained in the foregoing. After that, 4 parts of t-butyl
peroxy-2-ethylhexanoate was added to the mixture, and then the whole was
agitated by using a TK-homomixer at a number of revolutions of 12,000 rpm
with a high shear force so that a droplet of the polymerizable monomer
composition for a core was formed. The formed aqueous dispersion of the
monomer composition was put into a reaction vessel mounted with an
agitation blade, and then a polymerization reaction was initiated at a
reaction temperature of 90° C. When the polymerization conversion
degree reached substantially 100%, the aqueous dispersion of the
polymerizable monomer for a shell and 1 part of a 1% aqueous solution of
potassium persulfate were added to the resultant, and then the reaction
was continued for 5 hours. After that, the resultant was cooled to room
temperature at a rate of 10° C. per minute in order that the
reaction be stopped. Thus, an aqueous dispersion of core-shell type
polymer particles was obtained. The volume-average particle diameter (dV)
of core particles taken out immediately before the addition of the
polymerizable monomer for a shell was measured to be 7.1 μm, and the
ratio of the volume-average particle diameter to their number-average
particle diameter (dV/dP) was 1.26. The shell thickness was 0.12 μm,
the value obtained by dividing the longer radius of the toner by its
shorter radius (rl/rs) was 1.1, and the content of the toluene-insoluble
component was 5%.

[0273] While the aqueous dispersion of the core-shell type polymer
particles obtained in the foregoing was agitated, acid washing
(25° C., 10 minutes) was performed by setting the pH of the system
to 4 or less with sulfuric acid, and then water was separated by
filtration. After that, 500 parts of ion-exchanged water was newly added
to turn the remainder into slurry again, followed by water washing. After
that, dehydration and water washing were repeatedly performed again
several times, and then solid matter was separated by filtration. After
that, the solid matter was dried with a dryer at 45° C. for a
whole day and night. Thus, toner particles 28 were obtained.

[0274] 0.3 part of a colloidal silica (trade name: R-202, manufactured by
Degussa Co.) subjected to a hydrophobic treatment was added to 100 parts
of the toner particles 28 obtained in the foregoing, and then the
contents were mixed with a Henschel mixer. Thus, Toner 28 was prepared.
Tables 4 and 5 show the results.

[0275] Used as an image-forming apparatus was an LBP-3100 as modified so
that the process speed was 125 mm/sec and the abutment pressure between
the fixing film and the pressure roller was 7 kgf.

[0276] An image having a print percentage of 1% was printed with an
8-point `A` character under a normal-temperature, normal-humidity
environment (having a temperature of 25.0° C. and a humidity of
50% RH) by using Toner 1 in the image-forming apparatus. At this time,
image densities at an initial stage and when images were printed on 4,000
sheets according to an intermittent mode were each evaluated. It should
be noted that an A4 paper sheet (80 g/m2) was used as a recording
medium. As a result, high image densities were obtained throughout the
image output test, no density unevenness occurred, and dot
reproducibility was satisfactory. The image density at the time of the
termination of the test was 1.5 or more, which meant that the acquisition
of a high-quality image was attained. In addition, the fixing film was
observed after the 4,000-sheet image output test. As a result, no
contamination was found.

[0277] Further, the same image-forming apparatus was modified so that the
fixation temperature of the fixing unit could be adjusted, and then Toner
1 was evaluated for its fixability by using a Xerox paper sheet (75
g/m2) under a normal-temperature, normal-humidity environment
(having a temperature of 25.0° C. and a humidity of 50% RH). As a
result, the fixation lower limit temperature was less than 180°
C., which meant that satisfactory low-temperature fixability was
obtained. Table 6 shows the result.

[0278] Here, evaluation items described in the examples of the present
invention and the comparative examples, and evaluation criteria for the
items are described below.

(a) Image Density

[0279] Solid image portions were formed and evaluated at an initial stage
and after the termination of printout on 4,000 sheets. It should be noted
that their image densities were each a relative density of a printout
image measured with a "Macbeth Reflection Densitometer" (manufactured by
Gretag Macbeth Co.), which is an image density-measuring apparatus, with
respect to a white portion having a manuscript density of 0.00.

[0280] In addition, each of the produced toners was left to stand under a
42.0° C./95% RH environment for 30 days, and then solid image
portions were formed and evaluated at an initial stage after the standing
and after the termination of the printout.

A: 1.50 or more B: 1.40 or more and less than 1.50 C: 1.30 or more and
less than 1.40 D: Less than 1.30

(b) Density Unevenness

[0281] In the image output test, monochromatic solid images and halftone
images were printed out at an initial stage and after the termination of
printout on 4,000 sheets, and were then each visually evaluated for its
image uniformity.

A: The image is uniform and no image unevenness can be observed. B:
Slight image unevenness can be observed. C: Image unevenness can be
observed but is at a practically acceptable level. D: Remarkable image
unevenness can be observed.

(c) Dot Reproducibility

[0282] An evaluation for dot reproducibility was performed by observing
the presence or absence of defect black portions with a microscope at an
initial stage and after the termination of printout on 4,000 sheets in an
image output test using a checker pattern of 80 μm by 50 μm
illustrated in FIG. 4.

A: Two or less defect portions out of 100 portions. B: Three or more and
five or less defect portions out of 100 portions. C: Six or more and ten
or less defect portions out of 100 portions. D: Eleven or more defect
portions out of 100 portions.

(d) Contamination of Fixing Film

[0283] The condition where residual toner stuck to the surface of the
fixing film after the termination of the printout of solid images on
4,000 sheets, and the solid images were visually evaluated.

A: No contaminations occurred in the fixing film and the images. B:
Nearly no contaminations occurred in the fixing film and the images. C:
Contaminations occurred in the fixing film and the images, but were at
practically acceptable levels. D: A large number of contaminations
occurred in the fixing film and the images.

(e) Low-Temperature Fixability

[0284] Such an adjustment that the toner applied amount of an unfixed
image was 0.6 mg/cm2 was performed. After that, nine 5-cm square
solid images were output in an A4 paper sheet at each of fixation
temperatures set at a temperature increment of 5° C. in the
temperature range of 160° C. or more and 230° C. or less.
Each of the images was reciprocally rubbed with a lens-cleaning paper
sheet under a load of 4.9 kPa five times, and was then evaluated for its
fixation lower limit temperature, which was the temperature at which its
density reduced by 15% or more.

A: The fixation lower limit temperature is less than 180° C. B:
The fixation lower limit temperature is 180° C. or more and less
than 190° C. C: The fixation lower limit temperature is
190° C. or more and less than 200° C. D: The fixation lower
limit temperature is 200° C. or more.

Examples 2 to 19

[0285] Evaluations for developability at the initial stage and at the time
of long-term use, and an evaluation for fixability were performed under
conditions identical to those of Example 1 by using each of Toners 2 to
19 instead of Toner 1. As a result, image characteristics at the initial
stage were not problematic, and each of the toners results with no
serious problems till the termination of printout on 4,000 sheets. Table
6 shows the results of endurance evaluations under a normal-temperature,
normal-humidity environment.

Comparative Examples 1 to 9

[0286] Evaluations for developability at the initial stage and at the time
of long-term use, and an evaluation for fixability were performed under
conditions identical to those of Example 1 by using each of Toners 20 to
28 instead of Toner 1. As a result, each of Toners 20 to 28 was at a poor
level in terms of the contamination of the fixing film at the time of its
long-term use (after printout on 4,000 sheets). In addition, in each of
the evaluations of Toners 20 to 28, image deterioration at the time of
long-term use, an increase in fixation lower limit temperature, and the
contamination of the fixing film occurred, which affected printed images.
Table 7 shows the results of endurance evaluations under a
normal-temperature, normal-humidity environment.

[0287] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0288] This application claims the benefit of Japanese Patent Application
No. 2010-207641, filed Sep. 16, 2010, which is hereby incorporated by
reference herein in its entirety.